Crowley could sleep. He rather likes sleeping. Turning his mind off for a bit, letting dreams take over for a while. He's spent whole decades napping before and that's never been a problem for him. Can't exactly do that here, of course. Too much at stake to waste a few months or years asleep.

And that would mean less time with Aziraphale. He can't imagine sleeping away this time right now.

"Do you ever dream?" he asks. "Best part of sleeping, the dreaming part."