i have really bad nightmares too. it's been suggested to me to try altering the dreams - after all, you can do anything in a dream right? but i have been unsuccessful in this. i have worked instead on training myself to wake myself up when i have bad dreams. once i'm awake i can ground myself. then i usually need to read, or watch a show or something for a little while, just so i get something else on my mind before i try to go back to sleep. this makes for interrupted sleep, but it's worked better for me than anything else.