Yoga Nidra, which is derived from the tantras, is a powerful technique in which you learn to relax consciously. In Yoga Nidra, sleep is not regarded as relaxation. For absolute relaxation you must remain aware. This is a state of dynamic sleep, a systematic method of inducing complete physical, mental and emotional relaxation. The term Yoga Nidra is derived from two Sanskrit words, yoga meaning union or one-pointed awareness, and Nidra which means sleep. During the practice, one appears to be asleep, but the consciousness is functioning at a deeper level of awareness. Yoga Nidra is often referred to as psychic sleep or deep relaxation with inner awareness. In this threshold state between sleep and wakefulness, contact with the subconscious and unconscious dimensions occurs spontaneously.
During the practice, the state of relaxation is reached by turning inwards, away from outer experiences. If the consciousness can be separated from external awareness and from sleep, it becomes very powerful and can be applied in many ways, for example, to develop the memory, increase knowledge and creativity, or transform one's nature. In the raja yoga of Patanjali there is a state called pratyahara where the mind and mental awareness are dissociated from the sensory channels. Yoga Nidra is one aspect of Pratyahara which leads to the higher states of concentration and Samadhi.