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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]  

The term ‘Nidra’ means sleep (SAT-J.3)<ref>Available from  http://namstp.ayush.gov.in/#/sat</ref>. 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==

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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.<ref>Report on WHO technical meeting on sleep and health at Bonn Germany, 22-24 January 2004. Available from https://www.euro.who.int/__data/assets/pdf_file/0008/114101/E84683.pdf  accessed on 22/06/2021 </ref>

    

    

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]

==Etymology and derivation==

==Etymology and derivation==

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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”.<ref>Jha Srujan. Amarkosha online application</ref> It means sleep, sleepiness, sloth, dream, shutting, budding state, dead, dull, drowsiness etc.

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==Synonyms==

==Synonyms==

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

Shayanam, swapa, swapna/ swapnam, samvesha, tandra, supti,<ref>Jha Srujan. Amarkosha online application</ref> 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.<ref>Gillette M, Abbott S. Sleep Research Society. SRS Basics of Sleep Guide. Westchester, IL: Sleep Research Society; 2005. Fundamentals of the circadian system; pp. 131–138.</ref>

'''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.  

'''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.<ref>Saper CB, Cano G, Scammell TE. Homeostatic, circadian, and emotional regulation of sleep. Journal of Comparitive Neurology. 2005a;493(1):92–98.</ref>

'''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.  

'''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.<ref>Saper CB, Scammell TE, Lu J. Hypothalamic regulation of sleep and circadian rhythms. Nature. 2005c;437(7063):1257–1263.</ref>

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.  

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]

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 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).<ref>Cesar Timo-Iaria (in memorian); Angela Cristina do Valle, Physiology of dreaming,Sleep Science, Vol.2 Issue 2 / 2009 ,Available from:  http://sleepscience.org.br/details/145/en-US/physiology-of-dreaming</ref> 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.