Introduction :- Yoga nidra, which is derived from the tantras, is a powerful technique in which you relax consciously. In yoga nidra, sleep is not regarded as relxation. People feel that they are relaxing when collapse in an easy chair a with a cup of coffee, a drink or a cigarette, & read a newspaper or switch on the television. But this will never suffice as a scientific definition of relaxation. These are only sensory diversions. True relaxation is actually an experience far beyond all this. For absolute relaxation you must remain aware. This is yoga nidra, the state of dynamic sleep. Yoga nidra is a systematic method of inducing complete physical, mental & emotional relaxation. The term yoga nidra is derived from two Sanskrit words, yoga meaning union or one-pointed awareness, & nidra which means sleep. During the practice of yoga nidra, one appears to be asleep, but the consciousness is functioning at a deeper level of awareness. For this reason, yoga nidra is often referred to as psychic sleep or deep relaxation with inner awareness. In this threshold state between sleep & wakefulness, contact with the subconscious & unconscious dimensions occurs spontaneously. The birth of yoga nidra:- When I was living with my guru, Swami Sivananda, in Rishikesh, I had a very important experience which triggered my interest in developing the science of yoga nidra. I had been appointed to watch over a Sanskrit school where small boys were learning to chant the Vedas. It was my duty to remain awake all night to guard the school while the acharya was away. At three a.m. I used to fall into a deep sleep, & at six I would get up & return to the ashram. Meanwhile the boys got up at four, bathed & chanted Sanskrit prayers but I never heard them. The Art of Relaxation:- During the last hundred years or so the way of life has changed greatly throughout the world. The social system & other systems are no longer the same the same as they used to be in ancient times. This has brought about a dispersion of human energies at all levels. The mind of man has lost the point of balance & harmony in every sphere sphere of existence. We are so engrossed in material survival that we are not aware of what has been happening to us. Within the last century or two, diseases have sprung up with new dimensions, expressions & manifestions, & this has reached a peak in the few decades. Medical science has put an end to the great plagues of the past, but we are now faced with a new epidemic of stress-related disorders caused by our inability to adapt to the highly competitive pace of modern life. Training the Mind:- Yoga nidra means sleep with a trace of awareness. It is a state of mind in between wakefulness & dream. When you practice yoga nidra you are opening the deeper phases of your mind. At this moment, your intellectual mind is operating, but when you are able to relax, the subconscious & unconscious levels of the mind open. If you practice yoga nidra, then the nature of your mind can be changed, diseases can be cured, & your creative genius can be restored. The subconscious & the unconscious mind are the most powerful forces in the human being. This simple practice of yoga nidra has the capacity of penetrating into the depths of the human mind. Experiences in Yoga Nidra:- In what way does yoga nidra affect the body & mind? It can relax the whole system, awaken the psychic body, give one experiences of the astral plane, shift pressures from the coronary system & also exert an influence on the physical matter in the brain. When we practice yoga nidra, we are trying to transcend the behavior of the external mind. Various centres in the brain are stimulated systematically, so the experiences we undergo are natural. When the mind becomes subtle during the practice of yoga nidra, its experiences are almost on the same level as we have in dreams. There is, of course, the fundamental difference that the experiences in yoga nidra are much more vivid & clear than those that occur in the dreaming state.