Aziraphale thinks about it and tries to get into the bed, and though obviously he understands the concept of laying down and closing his eyes, somehow he lies there as if he is in a coffin, and his eyes do not close.

This is dreadfully boring, and he has so many other things that he could be doing, except that he can't leave Crowley's flat and he's already read the newspaper. Hardly anything could be more interesting today anyway than "The Armageddon happened."

So he tries, sliding his eyes closed, relaxing a bit. And maybe, just maybe, he falls asleep, and has a sweet dream, and shifts and gravitates towards Crowley once he's out warm.