Yog Nidra is a state of conscious deep sleep. One can say that it is a wholistic technique of relaxation. It helps in nurturing the seed of greater will power.Yog Nidra provides an incredible calmness, quietness and clarity. It is one of the deepest of all meditations, leading awareness through many levels of mental process to a state of supreme stillness.
It basically helps the person to inspire the higher self and enjoy the vitality of life. In a way it helps in regaining the point of balance and harmony in every sphere of existence.
Below mentioned link tell us about the various stages in yog nidra:-