Sri Aurobindo
Bases of Yoga
Bases of Yoga
It was not half sleep or quarter sleep or even one-sixteenth sleep that you had; it was a going inside of the consciousness, which in that state remains conscious but shut to outer things and open only to inner experience. You must distinguish clearly between these 
two quite different conditions, one is nidrā, the other, the beginning at least of samādhi (not nirvikalpa, of course!). This drawing inside is necessary because the active mind of the human being is at first too much turned to outward things; it has to go inside altogether in order to live in the inner being (inner mind, inner vital, inner physical, psychic). But with training one can arrive at a point when one remains outwardly conscious and yet lives in the inner being and has at will the indrawn or the outpoured condition; you can then have the same dense immobility and the same inpouring of a greater and purer consciousness in the waking state as in that which you erroneously call sleep.