No, but the materialist definition of "I" or 'mind' is the brain itself. If "I" is not present during sleep, then where did it go, if the brain is still active? If the brain is still active, then "I" should also be active. But what occurs is that the brain goes on a trip, creating fantasy images and scenarios for "I" IN THE ABSENCE OF CONSCIOUS ATTENTION. So if that is the case, maybe the "I" of the awakened state is also a fantasy-dream-sleep on a higher level. If you rely on the brain to provide a true picture of Reality, yet it does not during sleep, why would you trust it to do so during waking hours?
The past and currently sad condition of the world is a consequence of errors in judgment as dictated by the brain; by the "I". Obviously the brain does NOT provide a true picture of Reality, if the materialist view is a correct one. Why? Because the thinking mind creates concepts of Reality, which it then tries to superimpose over Reality as Reality itself. When they do not match, there is conflict. The "I" is self-centered, for the most part. Even when it seems to be altruistic, there are always ulterior motives involved. The "I" is still rooted in the old tribal brain which says: 'we vs. they', in which conflict is justified in the name of some glittering generality, like 'freedom', or 'democracy', or slogan like 'sempre fidelis', etc., adding a tone of nobility and pride to reinforce the reason for the conflict.
So, in both sleep and wakefulness, the brain fails to give us Reality. It is a limited mind which comes about, groping in the dark. Even science looks at the world in bits and pieces, never quite reaching a true understanding of what the whole of Reality actually is.
The experience of those who have seen these problems with the thinking mind have transcended the brain and it's offspring, the "I", to awaken a Higher Consciousness, one which, in spite of our broken world, does provide a true picture of Reality. Their descriptions of this experience are consistent one with the other even though they have been arrived at independently of each other, in different parts of the world, at different time in history. Their understanding of Reality is not a written, learned knowledge. It is just Reality as they awaken to it. It already IS, and is NOT a product of the brain; the brain is a product of Consciousness. As I mentioned before, this is suggested by recent scientific experiments of meditators whose cerebral cortexes are consistently thicker than those of non-meditators.