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Yoga nidra (Sanskrit: योग निद्रा) or yogic sleep is a state of consciousness between waking and sleeping, like the "going-to-sleep" stage. It is a state in which the body is completely relaxed, and the practitioner becomes systematically and increasingly aware of the inner world by following a set of verbal instructions. This state of consciousness (yoga nidra) is different from meditation in which concentration on a single focus is required. In yoga nidra the practitioner remains in a state of light pratyahara with four of his or her senses internalised, that is, withdrawn, and only the hearing still connects to the instructions. The yogic goal of both paths, deep relaxation (yoga nidra) and meditation are the same, a state called samadhi.
Yoga nidra is among the deepest possible states of relaxation while still maintaining full consciousness. In lucid dreaming, one is only, or mainly, cognizant of the dream environment, and has little or no awareness of one's actual environment.
The practice of yoga relaxation[clarification needed] has been found to reduce tension and anxiety. The autonomic symptoms of high anxiety such as headache, giddiness, chest pain, palpitations, sweating and abdominal pain respond well. It has been used to help soldiers from war cope with posttraumatic stress disorder (PTSD).
History and background-Edit
The concept of yoga nidra is very ancient in Indian traditions such as Hinduism and Buddhism. Krishna is often associated with yoga nidra in the epic Mahabharata. Similarly, many yogis and rishis are supposed to have experienced yoga nidra throughout their life.
In modern times, yoga nidra was experienced by Satyananda Saraswati when he was living with his guru Sivananda Saraswati in Rishikesh. He began studying the tantric scriptures and, after practice, constructed a system of relaxation, which he began popularizing in the mid-20th century. He explained yoga nidra as a state of mind between wakefulness and sleep that opened deep phases of the mind, suggesting a connection with the ancient tantric practice called nyasa, whereby Sanskrit mantras are mentally placed within specific body parts, while meditating on each part (of the bodymind). The form of practice taught by Satyananda includes eight stages (internalisation, sankalpa, rotation of consciousness, breath awareness, manifestation of opposites, creative visualization, sankalpa and externalisation).
Satyananda used this technique, along with suggestion, on the child who was to become his successor, Niranjanananda Saraswati, from the age of four. He claims to have taught him several languages by this method.
Anandmurti Gurumaa defines yoga nidra as a state of conscious deep sleep. One appears to be sleeping but the unconscious mind is functioning at a deeper level: it is sleep with a trace of deep awareness. In normal sleep we lose track of our self but in yoga nidra, while consciousness of the world is dim and relaxation is deep, there remains an inward lucidity and experiences may be absorbed to be recalled later. Since yoga nidra involves an aimless and effortless relaxation it is often held to be best practised with an experienced yoga teacher who verbally delivers instructions.
Anandmurti Gurumaa taught two techniques based on creative visualization. Yoga nidra as Yoga of Clear Light is proposed as a spiritual path (sadhana) in its own right, held to prepare and refine a seeker (sadhaka) spiritually, emotionally, mentally and physically for consciousness and awareness. The yogi may work through the consequences of deeds (karma), cleansing the store consciousness and purifying the unconscious mind. The state may lead to realisation (samādhi) and being-awareness-bliss (satchitananda). The yogi is held to be in communion with the divine. A tantrika engaged in this sadhana may become aware of past or future lives (refer bhumi) or experience the astral planes.
Experimental evidence of the existence of a fourth state of unified, transcendental consciousness, which lies in the yoga nidra state at the transition between sensory and sleep consciousness, was first recorded at the Menninger Foundation in Kansas, United States in 1971. Under the direction of Dr. Elmer Green, researchers used an electroencephalograph to record the brainwave activity of an Indian yogi, Swami Rama, while he progressively relaxed his entire physical, mental and emotional structure through the practice of yoga nidra. What they recorded was a revelation to the scientific community.  The swami demonstrated the capacity to enter the various states of consciousness at will, as evidenced by remarkable changes in the electrical activity of his brain. Upon relaxing himself in the laboratory, he first entered the yoga nidra state, producing 70% alpha wave discharge for a predetermined 5 minute period, simply by imagining an empty blue sky with occasional drifting clouds. Next, Swami Rama entered a state of dreaming sleep which was accompanied by slower theta waves for 75% of the subsequent 5 minute test period. This state, which he later described as being "noisy and unpleasant", was attained by "stilling the conscious mind and bringing forth the subconscious". In this state he had the internal experience of desires, ambitions, memories and past images in archetypal form rising sequentially from the subconscious and unconscious with a rush, each archetype occupying his whole awareness.
Finally, the swami entered the state of (usually unconscious) deep sleep, as verified by the emergence of the characteristic pattern of slow rhythm delta waves. However, he remained perfectly aware throughout the entire experimental period. He later recalled the various events which had occurred in the laboratory during the experiment, including all the questions that one of the scientists had asked him during the period of deep delta wave sleep, while his body lay snoring quietly.
Such remarkable mastery over the fluctuating patterns of consciousness had not previously been demonstrated under strict laboratory conditions. The capacity to remain consciously aware while producing delta waves and experiencing deep sleep is one of the indications of the third state (prajna) out of the total of four states of consciousness described in the Mandukya Upanishad. This is the ultimate state of yoga nidra in which there are no dreams, but only the deep sleep state with retained consciousness/awareness. The result is a single, semi-enlightened state of consciousness and a perfectly integrated and relaxed personality.
In 2006, Kamakhya Kumar was awarded a PhD by Dr. A. P. J. Abdul Kalam (former President of India) for his work "Psycho-physiological Changes as Related to Yoga Nidra". He observed six months of effects of yoga nidra on some physiological, hematological and some psychological parameters on the practitioners and he found a significant change on above mentioned parameters. One of the pieces of research published, was entitled "A study on the impact on stress and anxiety through yoga nidra" Indian Journal of Traditional Knowledge, Vol. 7 No 3 (Published through NISCAIR).
Indian clinical psychologist Sachin Kumar Dwivedi (2009) found in his research that yoga nidra decreases levels of anxiety. S. Dwivedi, S. Awasthi and B.B. Pandey (2011) found in "Yoga Nidra increased the α-EEG on α-EEG biofeedback", that it is an open secret that yoga nidra is a type of deep meditation. M. Nikhra and S.K. Dwivedi (2010) found in a study "Yoga Nidra Reduces the Level of Stress".
- Rivers, Eileen. A Breath of Hope. Washington Post Tuesday, May 6, 2008; Page HE01. http://www.washingtonpost.com/wp-dyn/content/article/2008/05/02/AR2008050203426.html
- Rama, Swami. Mandukya Upanishad: Enlightenment Without God. ISBN 0-89389-084-7.
- Saraswati, Swami Satyananda (1974). Tantra-yoga panorama. International Yoga Fellowship Movement. p. 25. Retrieved 8 March 2011.
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- Green, E.E., Biofeedback for mind/body self-regulation, healing and creativity, in Academy of parapsychology and medicine (1972). The varieties of Healing Experience: exploring psychic phenomena in healing; transcript of the interdisciplinary symposium, Los Altos - Calif., October 30, 1971. Retrieved 13 April 2011.
- Washington Post Article on study of Post Traumatic Stress Disorder using Yoga Nidra
- Science Direct Study of dopamine response during Yoga Nidra
- Human Brain Mapping Study using PET scans during Yoga Nidra
-  Yogа аnd Mеditаtion How to Guide 101
- Pictures of the brain's activity during Yoga Nidra Bindu Magazine article on Yoga Nidra research from The State University Hospital in Copenhagen.