Memories and dreams like that are very much apart of my life; it's keeping them from consuming my life, that's the fight. It's easier said than done. I'm going to be honest, the nightmares and flashbacks have gotten to the point where I'm really good at pretending I'm okay after only a minute long episode. Took me a while to get here.
I can say, however, that I have no idea how to make them stop. I'm just really good at grounding myself (most of the time, I'm not perfect). I don't know if your therapists have ever told you this, but don't use grounding techniques only during the memories/aftermath. Use them all of the time. When you're laying down, tense your body, every part starting from the neck down, then loosen up the same way. Cross your arms (at your forearms) and tap the opposite leg with the opposite hand, and count to 40 (this one's good when you feel one coming, during [if you can manage to think about it] and coming down from it). Count how many colors are in a room (outside), listen to every noise around you, feel different textured objects around the room with your hands. All of these are grounding techniques that I've learned in an effort to come down from flashbacks, keep flashbacks in check while going through them, and use prior when I feel one happening (which isn't always the case). You have to do these things when you feel fine as much as when you don't. To prep students for an emergency fire evacuation, schools burn the routine to evacuate inside students' skulls using fire drills. Your body will eventually remember, even when your mind won't.
Something else that can help a little is blasting music in my ears. I do it constantly throughout the day, it's rare when I don't have headphones or a radio blaring whatever song my little heart desires. Unfortunately, outside of Prazosin, I have no way to help you stop nightmares.
Let me know if you need any more tips or anything. I practically have a self-help manual for coping with PTSD, at this point with all of the articles I read and quote. Hopefully some of this will help.