I was just watching a an interview with a survivor of Auschwitz. She had terrible nightmares every night for years and years, even after marrying and having her own beloved children. Her husband brought her back to Auschwitz decades after the end of the war and she said after that the nightmares subsided because she could see that it was over and say goodbye to it.
I think that you have to find a way to say goodbye to the people and places where the traumas happened and that comes through many different ways for people—the grief work that you do for yourself and the younger parts who experienced it.
Yup when you find the cause (usually you will find the trauma its attached to) and understand what the nightmare is really telling you - it will likely go away.
The biggest problem is the mind messing part of PTSD.....one part hiding memories and the other part screaming for it to be found.
As far as nightmares, they happen and not much you can do to control it. Sleep tends to be the as big problem. Shower - get the sweat and stress hormones off, wash your sheets before the next night for the same reason. I always had a second place to nest and if not sleep at least rest - with something like a TV show or DVD I had seen a million times to have something for my brain to do and get bored with so maybe I could go back to sleep.
The one truism I found is - the more you worry about sleep the less sleep you get. So switch it up - celebrate the sleep you got, I know though its hard to celebrate 40 minutes sleep but work on being positive as you can about it.