and the fear makes you more anxious and more likely to be triggered into having a flashback or nightmare

Try doing a relaxation technique before bed - iaphramatic breathing is a good one - or if you are into visualisation - think of a blue light surrounding you protecting you from the nightmares -

I say to myself before I go to sleep that I am not going to have any nightmares tonight - sometimes it works

Fre-assuring yourself that this is the past that you survived it and so you can survive it now because its just replaying is another technique - getting up after the dream and doing something to take your mind off it also helps but it has to be relaxing

Hope things improve for you soon