Q: What happens to the consciousness of a realized one in sleep?
M: Such a question arises only in the minds of the unrealized. A jnani (one who has realized the Self)) has only one state, which is unbroken throughout the 24 hours, whether in what you call sleeping or waking. As a matter of fact, the majority of people are asleep, because they are not awake to the Self.
In the deep sleep state we lay down our ego, our thoughts and our desires. If we could only do all this while we are conscious, we would realize the Self.