Do Ghosts sleep? Do they dream?
Probably not, at least not in the same sense that humans do. They can rest, and seem to be able to be deactivated, and not even Ghosts themselves really know (or at least agree) what happens when they decompile away, but I don't think it's really the same thing as sleeping. It's possible that Ghosts can choose to imitate sleep or pretend to sleep if they want to for any reason (for example to rest or bond with people).
Sagira: I was hoping the Root Mind would take longer to get set up. But its Arc beam is at full intensity. It’ll be as tough as it was the first time.
Ghost: I wasn’t here for that. I think I was dead.
Sagira: Don’t be dramatic. You were asleep.
Ghost: I saw things in the dark. The Traveler was there. And it was so small.
When Sagira hijacked Ghost's shell, he was... Somewhere. In this dialogue, he considers that he may have been dead, but Sagira says he was just "asleep." He also notes that he was seeing things, kinda like a dream. But since nobody knows how the hell Sagira did this and how it worked, we have no way of knowing if Ghost being "asleep" is just a metaphorical thing she said or the closest analogy for what he was experiencing. Or if he truly was asleep. But even if he was, I don't think this is something Ghosts do as a part of their normal functioning.
