Hi,
I had a terrible car accident when I was a teen. Since that I have undiagnosed PSTD i believe. In addition to flashbacks I have night terrors. Like you I used to have a lot of those thoughts anticipating or fearing tragedy. Also I had unwanted physical reactions when being in a car with a bad driver or a driver that liked to speed. I never got therapy for PSTD. I managed to self-discipline those thoughts. When perceiving those thoughts coming to my mind I started regulating them: first, analyzing them, telling myself they were not rational. Then diverting my mind to other place, doing something, etc. during the time I lived overseas I used to call my mom everyday , but if I had those thoughts, I would call her again. It helped. I am not able to divert my thoughts related to depression, or, better said, I can do it, but only sometimes.
I was not trained to manage my thoughts although I think that all the years. I went to the church helped, as we used to do a lot of spiritual exercises