I'm sorry you are having such difficulties wiht nightmares and insomnia.
You've pretty much listed most everything I would suggest. The only other things I can think of are listening to relaxing music on a low volume (doesn't have to be traditionally seen as relaxing. you can listen to death metal if it's something that calms you). I've found when nothing else works, if I put a song on that "feels" relaxing in the moment, I can sleep a bit better. I pick songs based on what emotion is keeping me activated. Sometimes it's a song with lyrics that talk about safety, other times it's songs that talk about getting revenge, or being supported...

Have you had that PET scan? Any word on why you have been feeling so sick lately?