The study of Nidra in Ayurvedic perspective and its importance

: Ayurveda is the science of life and its main aim is to maintain healthy status of living being. Prevention and treatment of disease is the essence of Ayurveda. As per ayurvedic science, Nidra is one among most essential factors responsible for a healthy life. It is one of the Trayopsthambha . The lifestyle changes of this era have led to various disorders. The article lays emphasis on the ancient wisdom of Ayurveda about the importance of Nidra -physiological and critical review on study of Nidra . It also overviews and lights up the main study of Nidra already given in different ayurvedic texts. The ancient ayurvedic classics describes the 3 main milestones of life Ahara, Nidra and Brahmacharya. The entire study of Nidra and its classification is given in samhitas. The lifestyle changes have led to disorders like hypertension, obesity, diabetes mellitus and others. Good sleep is essential and advantageous to the quality of life. A number of vital physiological changes occur during sleep and help people stay healthy and function at their best. may be cognate with the English “drowsy” to be half


INTRODUCTION
The word Nidra derived from the prefix "Ni" is the Sanskrit root of our English word "Nether" or down as in "Nether world" (under world) While suffix "dra" may be cognate with the English "drowsy" to be half asleep, to be inactive or present an appearance of peaceful inactivity or isolation. According to Ayurveda, one should wake up at 'Brahma muhurta' sleep is an important phenomenon in our life as a part of normal physiology. Sleep is naturally occurring periodic state of rest of both body and mind, in which the eyes usually close and consciousness is completely or partially lost, with decreased bodily movement and decreased responsiveness to external stimuli. Sleep determines many aspects of our life like mood, cognitive functions such as attention and working memory, homeostasis etc.In metaphoric language it is called 'Vaishnavi maya' indicating that Nidra provides nutrition to maintain good health like Lord Vishnu (the sustaining god), who nourishes and sustains this world. Concept of sleep when the mind along with soul gets exhausted, or becomes stationary, and the sensory and motor organs also becomes inactive, the individual sleeps. Sleep occurs when the seat of Chetana (consciousness) is covered by Tamo guna (one among the the three main qualities of mind which is responsible for ignorance) which predominates along with Kapha. Sleep is another form of Tamas

MATERIALS AND METHODS
Materials related to Nidra and sleep physiology have been collected from different journals, Ayurvedic text books, authentic websites.

Definition of Nidra according to various
Acharyas: Acharya Charak-The mind and soul gets exhausted or becomes inactive and the sensory and motor organs become inactive then the individual gets sleep [1] Acharya Sushrut-Sleep occurs when the Hridaya, the seat of Chetana by Tamas [2] Acharya Dalhana, the commentator of Sushrut states-Nidra is the state of combination of mind and intellectual in which the person feels happy [3] Ashtang Sangrah-The Manovaha srotas become accumulated with Sleshma and mind is devoid of sense organs because of fatigue , when individual fell asleep [4] CLASSIFICATION OF NIDRA ACCORDING TO ACHARYAS [5] Charak Sushrut Vagbhat

REQUIREMENT OF SLEEP IN SATVIK, RAJASIK, TAMASIK PERSONS [6]
Satvik person -4-6 hrs of sleep Rajasik person -8 hrs of sleep Tamasik person-10-12 hrs of sleep IMPORTANCE OF NIDRA Acharya Sushruta in Chikitsa sthan said that "wholesome and timely sleep brings about homeostasis in bodily tissue." A person spends 1/3 rd of his life in sleep. So it is important to see that one gets a sound sleep at night [7] When the mind( as well as the soul) gets exhausted and the sensory and motor organs become inactive then the individual gets sleep. So when mind dissociates itself from some object, the person also dissociates from it. The sensory and motor organs are not active because of the inaction of individuals [8] Here, 'Manas' denote 'Internal senses' (Antahkarana) or self accompanied by manas. 'Karmatmanah' means senses or it may denote worldly souls [9] Happiness, misery, nourishment, emaciation, weakness, strength, virility, sterility, knowledge, ignorance, life and death all these occur depending on the proper or improper sleep. Like the night of destructions, untimely and excessive sleep and prolonged vigil take away both happiness and longevity [10] Sleep if properly enjoyed brings about happiness and longevity in human beings as the real knowledge brings about Siddhi(spiritual power) in a Yogi. During the summer in the day time one should sleep in an air cooled apartment. In the night, after having besmeared the body with sandal paste, one should sleep on the open airy roof of the house which is cooled by the rays of the moon. Those who take proper sleep in proper time will not suffer from disease, the mind of them will be peaceful, they gain strength and good complexion, good virility.Sleep used in the management of emaciation. Excessive, improper and sleeplessness leads to misery and finally to death. Proper sleep will make for happiness and long life just as the mind of the sages became clear from the knowledge of the soul.

SLEEPING PATTERN
After taking dinner, one should walk for 100 steps before going to sleep, then one should lie down inrecumbent posture up bed taking 8 times breath and should change the posture to right lateral till taking 16 times breath and thereafter to left lateral taking 32 times breath and then can sleep in any posture. But it is always advisable to sleep in left lateral because the Agni( digestive fire) lies in the left side of the body above the Nabhi(umbilicus) which is responsible for the digestion [11] TIME SUITABLE TO WAKE [11] Though the duration of sleep is not directly mentioned in the Ayurvedic classics but indirectly it can be understood by the verse given by Acharya Vagbhata, one should wake up in the Brahmamuhurta which is 48 minutes before sunrise following the proper digestion of food taken at night.

SUITABLE PLACE TO SLEEP
Effect of different kinds of beds used for sleeping on health has been described in details as follows: 1.

MODERN VIEW Physiology of sleep
When mind is fatigued then sleep occurs. According to Howell, sleep is due to cerebral ischemia. Cerebral cortex is the seat of higher centres like pre and post central gyrus and associated area etc. which have the correlation with mental activities described in Ayurveda. So due to the reduction in cerebral blood supply mind becomes calm that causes sleep [14] Physiological effects of sleep: Acharya Charak explains that in the night, Hridaya (Heart) gets contracted and the Srotasa (the channels of circulation) as well as the Koshtha (the gastro-intenstinal tract) are contracted , the body elements get softened [15] According to modern view, sleep causes two major types of physiological effects,  Effects on the Nervous System itself.  Effects on the other structures of the body.

Regulation of sleep
During wakefulness, the brain is kept in an alert state by the interactions of two major systems of nerve cells, in the upper part of the pons and in the midbrain, which makes acetylcholine as their neurotransmitter (NT) sends inputs to the thalamus to activate it. It in turn activates the cerebral cortex and produces a waking Electroencephalography (EEG) pattern. However, during Random Eye Movement (REM) sleep, the cholinergic nerve cells, thalamus and the cortex are in a condition, similar to wakefulness but the brain is in Random Eye Movement (REM) sleep. The difference is supplied by three sets of nerve cells in the upper part of the brain stem: The brain stem cell groups that control arousal are in turn regulated by two groups of nerve cells in the hypothalamus. One group of nerve cells, in the ventrolateral pre-optic nucleus, contains inhibitory NT(neurotransmitter) and GABA. The major influence on sleep cycle is the body's circadian rhythm, the suprachiasmatic nucleus. These nerve cells in the hypothalamus contain clock genes, which go through a biochemical cycle of almost exactly 24 hours sleep, hormones and other bodily functions [16] Depth of sleep The depth of sleep is not constant during the sleeping period, but varies from hour to hour. In most adults, sleep deepens rapidly to the end of the first hour, after which it lessens sharply for a time, and then more slowly till the time of waking. Generally, sleep taken during the daytime is lighter than that during the night [17]

DISCUSSION:
The important observation made during the study -Sleep is directly connected with mental state. Ayurveda emphasized that Sharira and Satva both interact with one another in all sphere of life. Sleep is particularly relevant to psychiatric illness and frequently part of diagnostic criteria for specific disorders. In today's era, people are not getting plenty hours of sleep because of busy life schedules and overload, as a result, work hours have engaged the time of sleep. Tension also contributed its share in reducing the sleeping time. If a healthy not getting proper sleep, he will become a patient. It is not a serious problem in the start. But later on it leads to number of health nuisance and ailments.

CONCLUSION:
All is well if someone sleeps well. To combat the lifestyle disorders and lead a healthy life, ideal Nidra plays an important role. Thus it is observed that the person have sufficient sleep according to the age, climatic, physical etc factor can attain positive energy and enthusiasm to perform work. And ultimately lead to a better and healthy life. Sleep is a chief nourisher at life's feast. It occurs due to increased Tamoguna. During sleep anabolism is active and catabolism relatively passive thus prevents body organs from damaged and repairs damage at cellular level. Thus sleep is essential for survival. Our Acharyas have already explained Nidra, its maintenance , also Anidra, its causes, diagnosis and treatment.