We're not fully alert while asleep, but still certainly conscious

This seems to require a rewrite of the usual dictionary understanding of conscious and unconscious. Sleep is a deeply altered state. I can still perceive stimuli, so that a loud noise or shake will wake me up, but I am not aware of any stimuli, or at least I don't remember them long. It seems like awareness is the main difference. I don't know I am sleeping; it is much like being dead.

The moment of discontinuity when uploading/encoding a consciousness into a new form may serve as barrier that we can never cross.

My friend Barış told me about his idea of a workaround the night before I had my lucid dream. He suggested that you could transfer the mind gradually. As you activate the neural mappings in the new substrate, you keep them wired to the old brain. You turn off the old nodes one by one as you turn on their new copies.

The conscious person would always have a complete, intact mind, and there be no awkward moments of non-existence or duplicate existence.

I didn't think it fair to criticize this plan on technological grounds, since there's no telling what will eventually be possible, but I thought of a laws-of-physics objection:

No matter how near you have the new mind matter, there will be some unavoidable lag in signals going back and forth to the old brain. Assuming that timing is critical in neural messaging, I conclude that the mind will become hopelessly jumbled and confused while it is divided across two locations. The process would be so disruptive that continuity of experience would be impossible.

Ever seen Altered States? Heh, interesting flick.

Added to my queue.

I do find it fascinating that humans are reportedly unable to cope with total silence.

I would like to give it a try too, but I wouldn't expect it to be so intolerable: "a mix of deep relaxation and temporal disorientation" sounds reasonable for anyone spending an hour wide awake in a dark room.