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The term ‘Nidra’ means sleep (SAT-J.3) . It is a natural physiological process that occurs in all living beings usually during the nights. It is essential for resting the body and mind after the day-long exertion. Sleep (nidra) is equally essential like food (ahara) and following the path of ultimate reality (brahmacharya). These three are three sub-pillars of life. [Cha. Sa. [[Sutra Sthana]] 11/35]

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==Importance of sleep in the preservation of health==

==Importance of sleep in the preservation of health==

Sleep is an important part of lifestyle. It is estimated that an average individual spends nearly one third part of life in sleeping. Sleep is a basic human need. It is essential for good health, good quality of life and performing well during the day. Sleep deprivation can lead to various physical effects  like sleepiness, fatigue, hypertension. It can cause cognitive impairments like deterioration of performance, attention, and motivation; diminishment of mental concentration, intellectual capacity, and mental health complications. Inadequate rest impairs the ability to think, handle stress, maintain a healthy immune system, and moderate emotions.  

Sleep is an important part of lifestyle. It is estimated that an average individual spends nearly one third part of life in sleeping. Sleep is a basic human need. It is essential for good health, good quality of life and performing well during the day. Sleep deprivation can lead to various physical effects  like sleepiness, fatigue, hypertension. It can cause cognitive impairments like deterioration of performance, attention, and motivation; diminishment of mental concentration, intellectual capacity, and mental health complications. Inadequate rest impairs the ability to think, handle stress, maintain a healthy immune system, and moderate emotions.

The sleeping urge is one among non-suppressible natural urges. [Cha. Sa. [[Sutra Sthana]] 7/ 3] Sleep is a function of the mind. All kinds of perception or connections with the external world are blocked in sleep. The mind is disconnected from all sensory and motor organs during sleep. [Patanjali Yoga Sutra 1/20]

The sleeping urge is one among non-suppressible natural urges. [Cha. Sa. [[Sutra Sthana]] 7/ 3] Sleep is a function of the mind. All kinds of perception or connections with the external world are blocked in sleep. The mind is disconnected from all sensory and motor organs during sleep. [Patanjali Yoga Sutra 1/20]

The normal sleep is responsible for happiness, nourishment, strength, virility, knowledge and liveliness. On the contrary, abnormal sleep can cause miseries, malnutrition, weakness, impotence, ignorance, and death. Untimely sleep, excessive and deprived can take away the good fortunes of life. Properly observed sleep can provide happiness. [Cha. Sa. [[Sutra Sthana]] 21/36-38] Those who resort to proper sleep are free from diseases, have pleasant attitudes, and are endowed with strength, complexion and virility. They are not too obese or too lean and have a longer lifespan with all prosperity. [Su. Sa. Sharira Sthana 4/39, 40]  

The normal sleep is responsible for happiness, nourishment, strength, virility, knowledge and liveliness. On the contrary, abnormal sleep can cause miseries, malnutrition, weakness, impotence, ignorance, and death. Untimely sleep, excessive and deprived can take away the good fortunes of life. Properly observed sleep can provide happiness. [Cha. Sa. [[Sutra Sthana]] 21/36-38] Those who resort to proper sleep are free from diseases, have pleasant attitudes, and are endowed with strength, complexion and virility. They are not too obese or too lean and have a longer lifespan with all prosperity. [Su. Sa. Sharira Sthana 4/39, 40]  

Food and sleep are the determinants of obesity and emaciation. [Cha. Sa. [[Sutra Sthana]] 21/51] Night vigil causes dryness in body, while day sleep causes unctuousness. This leads to the aggravation of [[vata dosha]] and [[kapha dosha]] respectively. Sleeping in a sitting posture does not influence dosha equilibrium. It causes neither too dryness nor unctuousness. [Cha. Sa. [[Sutra Sthana]] 21/50]  

 

Food and sleep are the determinants of obesity and emaciation. [Cha. Sa. [[Sutra Sthana]] 21/51] Night vigil causes dryness in body, while day sleep causes unctuousness. This leads to the aggravation of [[vata]] [[dosha]] and [[kapha]] [[dosha]] respectively. Sleeping in a sitting posture does not influence [[dosha]] equilibrium. It causes neither too dryness nor unctuousness. [Cha. Sa. [[Sutra Sthana]] 21/50]  

This article deals with the physiology of sleep, its classification, and its importance in healthy and diseased conditions described in Ayurveda texts.  

This article deals with the physiology of sleep, its classification, and its importance in healthy and diseased conditions described in Ayurveda texts.  

==Etymology and derivation==

==Etymology and derivation==

The word is derived from the Sanskrit word root “Nidi kutsyaayaam” by adding the suffix “rak”.  It means sleep, sleepiness, sloth, dream, shutting, budding state, dead, dull, drowsiness etc.

The word is derived from the Sanskrit word root “Nidi kutsyaayaam” by adding the suffix “rak”.  It means sleep, sleepiness, sloth, dream, shutting, budding state, dead, dull, drowsiness etc.

==Synonyms==

==Synonyms==

Shayanam, swapa, swapna/ swapnam, samvesha, tandra, supti,  vaishnavi [Su. Sa. [[Sharira Sthana]] 4/33]

Shayanam, swapa, swapna/ swapnam, samvesha, tandra, supti,  vaishnavi [Su. Sa. [[Sharira Sthana]] 4/33]

==Physiology of sleep==  

==Physiology of sleep==  

When the mind and body are tired, [[kapha]] [[dosha]] and inertia (tamas guna) are increased in the body. In this state, the sensory organs are unable to function. This state leads to sleep (nidra). [Cha. Sa. [[ Sutra Sthana]] 21/35] Inertia (tamas) is the prime factor responsible for sleep (nidra). [Su. Sa. [[Sharira Sthana]] 4/34]

When the mind and body are tired, [[kapha]] [[dosha]] and inertia (tamas guna) are increased in the body. In this state, the sensory organs are unable to function. This state leads to sleep (nidra). [Cha. Sa. [[ Sutra Sthana]] 21/35] Inertia (tamas) is the prime factor responsible for sleep (nidra). [Su. Sa. [[Sharira Sthana]] 4/34]

The interplay of two significant processes regulates the sleep-wake system.  

The interplay of two significant processes regulates the sleep-wake system.  

a) Process S is the homeostatic drive for sleep. It is regulated by the neurons found in the preoptic area of the hypothalamus of the brain. These neurons contain molecules that inhibit neuronal communication and turn off the arousal systems during sleep.  

 

b) Process C promotes wakefulness and alertness. The circadian system regulates it. Wakefulness is generated by an ascending arousal system from the brainstem. This activates forebrain structures by transmitting sensory information to the cerebral cortex and activating the nerve cells to interpret and analyze the sensory inputs.  

a)Process S is the homeostatic drive for sleep. It is regulated by the neurons found in the preoptic area of the hypothalamus of the brain. These neurons contain molecules that inhibit neuronal communication and turn off the arousal systems during sleep.  

 

b)Process C promotes wakefulness and alertness. The circadian system regulates it. Wakefulness is generated by an ascending arousal system from the brainstem. This activates forebrain structures by transmitting sensory information to the cerebral cortex and activating the nerve cells to interpret and analyze the sensory inputs.  

 

Through the synchronization of the circadian system, process C assists in keeping sleep-wakefulness cycles coordinated with environmental light-dark cycles.  

Through the synchronization of the circadian system, process C assists in keeping sleep-wakefulness cycles coordinated with environmental light-dark cycles.  

Process S is similar to the functions of [[kapha dosha]] and [[tamas guna]] that promotes sleep. Process C is similar to functions of [[vata dosha]] and [[rajo guna]] that promotes wakefulness.

 

Role of the mental constitution:  

Process S is similar to the functions of [[kapha]] [[dosha]] and [[tamas]] [[guna]] that promotes sleep. Process C is similar to functions of [[vata]] [[dosha]] and [[rajo]] [[guna]] that promotes wakefulness.

The mental constitution of a person can influence natural sleep patterns variably.  

 

a) In [[tamo guna]] predominant people, sleep occurs excessively during both the day and night.

===Role of the mental constitution:===

b) In [[rajo guna]] predominant people, sleep is irregular and can occur at any time, day or night.  

 

c) In [[sattva guna]] predominant people, sleep occurs at midnight only. [Su. Sa. Sharira Sthana 4/33,Dalhana]

The mental constitution of a person can influence natural sleep patterns variably.

Dreams (swapna)

The dreams are seen due to the association of the mind with [[rajo guna]]. It perceives both auspicious and inauspicious objects of senses based on previous experiences in the form of dreams. [Su.Sa.Sharira Sthana 4/36-37]  

a)In [[tamo guna]] predominant people, sleep occurs excessively during both the day and night.

When the mind continues to cognize, the sleeping person experiences different kinds of dreams. The sense organs are not receptive to their perceptions in this state. [A.S. Sutra Sthana 9/21]  

 

A dream is a conscious experience that occurs during sleep. Although it may happen in any sleep phase, it prevails during the desynchronized phase (REM type).   

b)In [[rajo guna]] predominant people, sleep is irregular and can occur at any time, day or night.  

Like any information consciously identified, a dream triggers a specific behavior, that we call an oneiric behavior. It comprises two types of identifiable manifestations:  

 

c)In [[sattva guna]] predominant people, sleep occurs at midnight only. [Su. Sa. Sharira Sthana 4/33,Dalhana]

 

===Dreams (swapna)===

The dreams are seen due to the association of the mind with [[rajo guna]]. It perceives both auspicious and inauspicious objects of senses based on previous experiences in the form of dreams. [Su.Sa.Sharira Sthana 4/36-37]

When the mind continues to cognize, the sleeping person experiences different kinds of dreams. The sense organs are not receptive to their perceptions in this state. [A.S. Sutra Sthana 9/21]

A dream is a conscious experience that occurs during sleep. Although it may happen in any sleep phase, it prevails during the desynchronized phase (REM type).  Like any information consciously identified, a dream triggers a specific behavior, that we call an oneiric behavior. It comprises two types of identifiable manifestations:  

 

a) Motor: These components are usually weak and poorly expressed movements during a dream.

a) Motor: These components are usually weak and poorly expressed movements during a dream.

b)Vegetative: Phasic increases heart rate, blood pressure, respiration, pupillary diameter, and metabolic adjustments, which are expressed more consistently during a dream, as they are during attentive wakefulness.  

 

b)Vegetative: Phasic increases heart rate, blood pressure, respiration, pupillary diameter, and metabolic adjustments, which are expressed more consistently during a dream, as they are during attentive wakefulness.

==Types of sleep==

==Types of sleep==

Sleep is broadly classified into three types based on its fundamental cause.

Sleep is broadly classified into three types based on its fundamental cause.

a) Natural sleep (swabhaviki nidra): This occurs in a healthy individual as a natural process.

 

b) Abnormal sleep/insomnia (vaikariki nidra): The abnormal sleep occurs due to aggravated [[vata dosha]] and depleted state of [[kapha dosha]]. It is also caused due to various ailments of the mind and body. This is known as vaikariki nidra.

a)Natural sleep (swabhaviki nidra): This occurs in a healthy individual as a natural process.

c) Sleep due to inertia (tamasi nidra): When channels carrying sensory perceptions are filled with excess inertia (tamo guna) and predominant [[kapha]], it leads to “tamasi nidra”. This type is seen at the time of death. It is difficult to awaken the person in this state.  [Su.Sa. Sharira Sthana 4/33, Dalhana]  

 

b)Abnormal sleep/insomnia (vaikariki nidra): The abnormal sleep occurs due to aggravated [[vata dosha]] and depleted state of [[kapha dosha]]. It is also caused due to various ailments of the mind and body. This is known as vaikariki nidra.

 

c)Sleep due to inertia (tamasi nidra): When channels carrying sensory perceptions are filled with excess inertia (tamo guna) and predominant [[kapha]], it leads to “tamasi nidra”. This type is seen at the time of death. It is difficult to awaken the person in this state.  [Su.Sa. Sharira Sthana 4/33, Dalhana]  

 

There are two types of sleep based on electroencephalographic (EEG) observations during sleep.

There are two types of sleep based on electroencephalographic (EEG) observations during sleep.

a) Non-rapid eye-movement (NREM) sleep  

a) Non-rapid eye-movement (NREM) sleep  

b) Rapid eye-movement (REM) sleep.

b) Rapid eye-movement (REM) sleep.

NREM sleep is divided further into four stages based on variations in brain wave patterns, eye movements, and muscle tone. In the course of a period of sleep, NREM and REM sleep alternate cyclically. A normal sleep episode begins with a short period of NREM stage 1, progressing through stage 2, followed by stages 3 and 4, and finally to REM. The individuals do not remain in REM sleep throughout the night. The cycle between the stages of NREM and REM continues.  NREM sleep constitutes about 75 -80% of the total duration of sleep, and REM sleep constitutes the remaining 20 – 25%. The function of cyclic change between these two types of sleep is not yet understood. However, irregular cycling or absent sleep stages are associated with sleep disorders.  E.g. Individuals with narcolepsy enter sleep directly into REM sleep instead of entering sleep through NREM.  

 

NREM sleep is divided further into four stages based on variations in brain wave patterns, eye movements, and muscle tone. In the course of a period of sleep, NREM and REM sleep alternate cyclically. A normal sleep episode begins with a short period of NREM stage 1, progressing through stage 2, followed by stages 3 and 4, and finally to REM. The individuals do not remain in REM sleep throughout the night. The cycle between the stages of NREM and REM continues.  NREM sleep constitutes about 75 -80% of the total duration of sleep, and REM sleep constitutes the remaining 20 – 25%. The function of cyclic change between these two types of sleep is not yet understood.

 

However, irregular cycling or absent sleep stages are associated with sleep disorders.  E.g. Individuals with narcolepsy enter sleep directly into REM sleep instead of entering sleep through NREM.  

 

There are seven types of sleep based on the causes of sleep.  

There are seven types of sleep based on the causes of sleep.  

1)Originated from inertia (tamobhava)

 

1)Originated from inertia (tamobhava)

 

2) Originated from [[kapha]] (shleshmasmudbhava)

2) Originated from [[kapha]] (shleshmasmudbhava)

3) Due to mental exertion (mana shrama sambhava)

3) Due to mental exertion (mana shrama sambhava)

4) Due to physical exertion (sharira shrama sambhava)

4) Due to physical exertion (sharira shrama sambhava)

5) Due to exogenous factors (agantuki)

5) Due to exogenous factors (agantuki)

6) Associated with diseases (vyadhyanuvartini)

6) Associated with diseases (vyadhyanuvartini)

7) Normal sleep at night (ratri swabhava prabhava) [Cha. Sa. [[Sutra Sthana]] 21/58]  

 

7) Normal sleep at night (ratri swabhava prabhava) [Cha. Sa. [[Sutra Sthana]] 21/58]

The sleep patterns in the above types of sleep are yet to be explored through research studies.

The sleep patterns in the above types of sleep are yet to be explored through research studies.

== Diagnosis of sleep disorders ==

== Diagnosis of sleep disorders ==

Sleep is an important parameter to assess the health status of a person. Sleep patterns are affected during different disease conditions.

Sleep is an important parameter to assess the health status of a person. Sleep patterns are affected during different disease conditions.

• Loss of sleep (nidra nasha) is due to aggravation of [[vata]] [[dosha]] [ A. Hr. Sutra Sthana 11/6]

 

• Decrease in sleep duration (alpa nidra) is due to aggravation of [[pitta]] [[dosha]] [ A. Hr. Sutra Sthana 11/7]

*Loss of sleep (nidra nasha) is due to aggravation of [[vata]] [[dosha]] [ A. Hr. Sutra Sthana 11/6]

• Increase in sleep duration (atinidra) is due to aggravation of [[kapha]] [[dosha]] [A. Hr. Sutra Sthana 11/8]

 

In contemporary views, sleep disorders include the following conditions:  

*Decrease in sleep duration (alpa nidra) is due to aggravation of [[pitta]] [[dosha]] [ A. Hr. Sutra Sthana 11/7]

• Insomnia

 

• Sleep-related breathing disorders like sleep apnoea  

*Increase in sleep duration (atinidra) is due to aggravation of [[kapha]] [[dosha]] [A. Hr. Sutra Sthana 11/8]

• Central disorders of hypersomnolence  

 

• Circadian rhythm sleep–wake disorders,

In contemporary views, sleep disorders include the following conditions:

• Parasomnias  

• Sleep-related movement disorders and other sleep disorders.  

*Insomnia

As per Ayurveda, the clinical presentations of sleep disorders may be broadly classified into two types.

 

a) Excessive sleep (ati nidra)

*Sleep-related breathing disorders like sleep apnoea

b) Loss of sleep/insomnia (anidra)

*Central disorders of hypersomnolence  

 

*Circadian rhythm sleep–wake disorders

*Parasomnias  

 

*Sleep-related movement disorders and other sleep disorders.  

 

As per Ayurveda, the clinical presentations of sleep disorders may be broadly classified into two types.

a)Excessive sleep (ati nidra)

 

b)Loss of sleep/insomnia (anidra)

===Causes of excessive sleep===

===Causes of excessive sleep===

Excess consumption of fats in the diet causes excess accumulation of fat ([[meda]]) and [[kapha dosha]]. This leads to obstruction in body channels, heaviness in the body and lethargy. This causes excessive sleep or hypersomnolence. [A. Sa. Sutra Sthana 9/30-33]

Narcolepsy is a chronic neurological disorder that affects the brain’s ability to control sleep-wake cycles. People with narcolepsy have excessive, uncontrollable daytime sleepiness. They may also suddenly fall asleep at any time, during any kind of activity. The exact cause of narcolepsy is unknown in contemporary sciences. People with type 1 narcolepsy have low levels of the chemical hypocretin, which is an important neurochemical that regulates wakefulness and REM sleep.  The relation between high-fat diet and narcolepsy needs further research.  

Excess consumption of fats in the diet causes excess accumulation of fat ([[meda]]) and [[kapha dosha]]. This leads to obstruction in body channels, heaviness in the body and lethargy.This causes excessive sleep or hypersomnolence. [A. S. Sutra Sthana 9/30-33]

 

Narcolepsy is a chronic neurological disorder that affects the brain’s ability to control sleep-wake cycles. People with narcolepsy have excessive, uncontrollable daytime sleepiness. They may also suddenly fall asleep at any time, during any kind of activity. The exact cause of narcolepsy is unknown in contemporary sciences. People with type 1 narcolepsy have low levels of the chemical hypocretin, which is an important neurochemical that regulates wakefulness and REM sleep.  The relation between high-fat diet and narcolepsy needs further research.  

=== Causes of insomnia ===

=== Causes of insomnia ===

• Emotional states of fear, worry, anger, happiness, grief, anxiety

• Excessive smoking, exercise, fasting, exertion, sexual intercourse

*Emotional states of fear, worry, anger, happiness, grief, anxiety

• Excessive hunger, excessive intake of dry food

 

• Lapse of the standard sleeping time and habit

*Excessive smoking, exercise, fasting, exertion, sexual intercourse

• Other mechanical factors like uncomfortable bed, atmosphere etc.

 

• Increased [[sattva guna]] and decreased [[tamas]]  

*Excessive hunger, excessive intake of dry food

• Old age

 

• Excess administration of procedures like therapeutic purgation ([[virechana]]), emesis ([vamana]]), nasal errhines ([[nasya]]), blood-letting ([[raktamokshana]])

*Lapse of the standard sleeping time and habit

• [[Vata dosha]] predominant diseases, [[vata dosha]] dominance in basic body constitution ([[prakriti]]), aggravation of [[vata]] / [[vata]] along with [[pitta]] in the body due to any cause

 

                                        [Cha.Sa.[[Sutra Sthana]]21/55-57], [A. S. Sutra Sthana 9/34-36]

*Other mechanical factors like uncomfortable bed, atmosphere etc.

Research shows an increased prevalence of insomnia in women and older adults. In women, insomnia is more prevalent during menarche and menopause.  Comorbid medical disorders,  psychiatric disorders , and night duties or rotating shifts are significant risks for insomnia.

 

*Increased [[sattva guna]] and decreased [[tamas]]  

 

*Old age

 

*Excess administration of procedures like therapeutic purgation ([[virechana]]), emesis ([vamana]]), nasal errhines ([[nasya]]), blood-letting ([[raktamokshana]])

 

*[[Vata dosha]] predominant diseases, [[vata dosha]] dominance in basic body constitution ([[prakriti]]), aggravation of [[vata]] / [[vata]] along with [[pitta]] in the body due to any cause[Cha.Sa.[[Sutra Sthana]]21/55-57], [A. S. Sutra Sthana 9/34-36]

 

Research shows an increased prevalence of insomnia in women and older adults. In women, insomnia is more prevalent during menarche and menopause.  Comorbid medical disorders,  psychiatric disorders, and night duties or rotating shifts are significant risks for insomnia.

===Clinical features of insomnia ===

===Clinical features of insomnia ===

Loss of sleep causes body ache, heaviness in the head, frequent yawning, stiffness, tiredness, giddiness, impaired digestion, stupor, and other [[vata]] predominant diseases. [A.S. Sutra Sthana 9/37] Suppression of natural sleep urge causes frequent yawning, body ache, stupor, diseases of head, and heaviness of eyes. [Cha. Sa. [[Sutra Sthana]] 7/23]

Loss of sleep causes body ache, heaviness in the head, frequent yawning, stiffness, tiredness, giddiness, impaired digestion, stupor, and other [[vata]] predominant diseases. [A.S. Sutra Sthana 9/37] Suppression of natural sleep urge causes frequent yawning, body ache, stupor, diseases of head, and heaviness of eyes. [Cha. Sa. [[Sutra Sthana]] 7/23]

The persons with insomnia can develop the conditions causing hypoxemia and dyspnoea, gastroesophageal reflux disease, pain conditions, and neurodegenerative diseases.  Among the primary sleep disorders, restless legs syndrome (RLS), periodic limb movement disorders (PLMD), and sleep-related breathing disorders (snoring, dyspnoea, sleep apnoea) often present with an insomnia symptom.  

The persons with insomnia can develop the conditions causing hypoxemia and dyspnoea, gastroesophageal reflux disease, pain conditions, and neurodegenerative diseases.  Among the primary sleep disorders, restless legs syndrome (RLS), periodic limb movement disorders (PLMD), and sleep-related breathing disorders (snoring, dyspnoea, sleep apnoea) often present with an insomnia symptom.  

Research shows a relationship between inadequate sleep and medical conditions like hypertension,  obesity and type-2 diabetes, cardiovascular disease and arrhythmias,  mood disorders,  neurodegeneration and dementia,   and impaired immune functioning.  

Research shows a relationship between inadequate sleep and medical conditions like hypertension,  obesity and type-2 diabetes, cardiovascular disease and arrhythmias,  mood disorders,  neurodegeneration and dementia,and impaired immune functioning.  

== Untimely sleep (akala nidra) ==

== Untimely sleep (akala nidra) ==

Excess sleep during daytime is contraindicated in a healthy person. It provokes three [[dosha]] and can cause many ailments such as cough, respiratory discomforts, rhinitis, heaviness of head, body pain, anorexia, fever, impaired digestive power etc. [Su.Sa. Sharira Sthana 4/38]

Excess sleep during daytime is contraindicated in a healthy person. It provokes three [[dosha]] and can cause many ailments such as cough, respiratory discomforts, rhinitis, heaviness of head, body pain, anorexia, fever, impaired digestive power etc. [Su.Sa. Sharira Sthana 4/38]