You need to find something to distract you from your thoughts. Take a warm bath, take a walk and don't just walk but pay attention to every single step. Close your eyes and take three, four deep breaths and pay attention exclusively to your breathing. When you start thinking of something else, acknowledge you're thinking of it and then start thinking of your breathing again. Try some short, guided meditations from www.audiodharma.com. They start at only 3-4 minutes long and build from there. You can also download meditation apps on to a phone of tablet. I'm not saying this is an easy fix. I'm not telling you to "snap out of it" like so many like to do. I know how impossible that can be, but if you can distract your mind to think of something else and focus on the minute now, what's going on in the here and now and stop dwelling on the past, it will relieve your burden and allow you to have better control. Good luck. I know how hard it is at times. It's much easier for me to give advice than take it. When we get in "one of those moods" we often feel as though we deserve to suffer and we won't do things that will help. You deserve to feel better. Try some of those things, and best of luck. Free free to write if you want to.