Yoga nidra, “yogic sleep,” has several meanings: 1) a state of half-contemplation and half-sleep; 2) light yogic sleep when the individual retains slight awareness; 3) a state between sleep and wakefulness; 4) the state in which the yogi experiences pure consciousness within the state of dreamless sleep, when he is neither awake nor asleep in the usual sense; 5) the state in which the three states of waking, sleep, and deep sleep have become transmuted into the turiya state of pure consciousness and the yogi remains “asleep” in relation to those three lesser states. The fifth is the highest and the most important for the yogi.
In meditation we must consciously “sleep” in yoga nidra, resting in the mind as the inner, silent witness.
Yoga nidra is being fully conscious in the deep (dreamless) sleep state, or sushupti, in meditation while fully awake. At first glance this may just seem a bit of exotic trivia, but if we ponder it well we can understand that such ability is no doubt the basis of Krishna’s description of an enlightened yogi or one nearing that state. When we read in the Gita about how the yogi is to be unmoved by that which normally greatly affects the individual human being, we think of it being some powerful control and suppression of thought and feeling through conscious will. But actually it is awake yoga nidra. One who rests in the unchanging Self is not agitated by anything.
Next in Living the Yoga Life: The Yogi