Thank you for all the helpful suggestions and commiseration.

Unfortunately, exercise doesn't seem to do anything. He swam and played in the pool for several hours in 100+ degree heat yesterday and had his worst night yet.

I did buy a night light, and although he loves it, it doesn't seem to help.

We've also checked out some books from the library on how to deal with fears and anxiety but don't seem to be making any progress there either. Last night he had a complete meltdown.

It's looking more and more like he just doesn't want to be left alone in his bedroom at night. He doesn't want us to leave his room until he's "ready" (meaning has the sheet wrapped around him just so), but it's taking him longer and longer to get "ready" every night, so I'm starting to think it's just an excuse to keep us there. Last night, as a last resort, we ended up sitting with him until he fell asleep at bedtime and then again at 3 am.

Tonight I'm going to try playing classical music in his room to see if that helps make him feel less alone and vulnerable. The thought of having to stay with him until he's asleep brings back chilling memories of his first year, when he tried to kill us both by sleep deprivation! There's a reason he's an only child. Can't go back there!