Emotions can be tricky for me sometimes, especially when they run counter to what I know is true. What helps me is to remind myself of that truth and work on getting myself into a better frame of mind. I get some bad dreams too at times, I had a whopper of a nightmare just last night.
I usually sleep like a baby but if I'm under alot of stress my dreams may reflect that. It's a win-win situation for me to keep watch on what thoughts I allow to rule in my mind. It doesn't guarantee that I'll have overnight success (no pun intended) in stopping nightmares- but it fits right into the part of the Serenity Prayer to change what I can.