Since everyone is telling you to find some kind of therapy, if you don't think this is an option, try looking up some CBT worksheets and physically (with pen and paper) completing them. They should have 4-6 sections with titles like "immediate thought" "trigger" "emotion" etc etc.

Other things to look up would be PTSD coping mechanisms, but you will need to address these thoughts and recognize them as not harmful to where you are now. Which is what the sheets will help with. My favourite coping mechanism for when intrusive thoughts hit was to count objects in the room: "lamp, chair, book, Xbox, lamp, chair, book Xbox etc.". Other options are to run your hands up and down your arms/legs to remind yourself you are "here". Not anywhere harmful. There are many many coping mechanisms, but like I said, those thoughts may need to be addressed. And then you can move on and live your life.