I get paranoid thinking sometimes, too. The thing that helps the most is recognizing it as such. As soon as I notice the thought pattern, the thoughts may not go away immediately, but I can easily ignore them. I say to my brain, "i am choosing to move on". It somehow lets me acknowledge the thoughts, assign them no real meaning, and continue on doing whatever I need to without them dominating me. Sometimes I have to give myself some quiet time to process and move on, but it is getting easier and faster the more i do it.