This sounds really silly but it has helped me. I have/mostly used to have PTSD related nightmares. They tend to play on a loop and for a long time scared me badly enough I just did not want to sleep (not good for someone who is heading for a bipolar diagnosis). My therapist told me to think of something I was looking for in the dream, like the purple socks with green polka dots, and to remind myself before I went to sleep to look for that. I did, I would typically see the socks and the nightmare part would end or I'd wake up enough to turn over and go back to sleep without the dream. I did not believe it would help but it did. It's worth a try at least just because it doesn't cost anything.