Yoga Nidra is a guided relaxation technique that calms the physical body, nervous system, and subconscious mind. Developed by Swami Satyananda Saraswati and described in his book, Yoga Nidra, characteristic features of this practice are the use of sankalpa (positive intention), systematic rotation of consciousness throughout the body, and visualization. Studies show that one hour of yoga nidra practice has the regenerative effects of four hours of restful sleep.
Yoga Nidra does not require the practice of asana (other than the ability to get down into savasana and up again). It is appropriate for all levels.