In deep sleep, it seems to be a state of no consciousness. In the waking this is cruciel. It's because in the waking we have insufficiently distinguished consciousness from the mind. Not to go into it, ther no otherwatevedanta is possible. From the waking state of the mind. Its only say something about the mind which is shut down.
Inspired by the 15th chapter of the Ashtavakra Gita, Swami Sarvapriyananda gives a discourse on the nature of the Self.