Yoga Nidra in Hinduism is a kind of sleep induced by the technique of yoga. There is a difference between ordinary sleep and psychic sleep in yoga nidra. In sleep there is no awareness, whether internal or external; in yoga nidra, on the other hand, there is wakefulness to the internal environment. No difference, however, will be detected by an external observer.
Yoga Nidra is a method of exploring the different layers of the mind. According to certain schools of modern psychology, there are three dimensions of mind – the conscious, the subconscious and the unconscious. Mandukya Upanishad also classifies the mind into three layers – jagrat, swapna and sushupti. The yogic and psychological terminology can be related as follows:
Jagrat – conscious mind, waking state, surface thoughts and perception of the outside world; sthula (gross dimension)
Yoga Nidra starts from swapna state – that is exploration of the subconscious mind. If one masters yoga nidra, then the depth of perception may become deeper so that one contacts and explores ‘sushupti’ or cosmic mind. Great yogis go even further; they transcend the mind. They enter the state of super consciousness.
In Mandukya Upanishad, this state is called turiya (the fourth dimension of being). This is the highest state of yoga nidra, which few attain. It is real yoga nidra in the form of pure, illumined consciousness. Hence, it is not part of prakriti (nature) but is the manifested form of purusha (consciousness).
Yoga nidra involves nine stages, including relaxation of the body and the mind. The physical posture in yoga nidra should be sufficiently comfortable as to make the body feel more the ‘shell’ or ‘husk’ of the mind. Yoga nidra is a natural method of relaxing the mind and body, for combating many physical and psychosomatic diseases.