So as someone who semi-regularly gets bouts of shitty nightmares I can give you a little advice on how I help to stop them at least. It sounds really cliche but try to get a set sleeping pattern in place with a specific time you will be in bed from. You will want to make sure you are not playing around on a phone, or similar, for at least an hour before you go to sleep and likewise make sure you have not eaten any food too recently.  You basically want to get your body into the most calm and relaxed state as you can without it needing to be forced into it. If getting the above down doesn't work, then you will likely want to talk to someone you know about them, a friend perhaps, so that you can actually process through them and just 'get the ideas out of your head' as it were.