I worry and think of bad stuff too. When I worry too much, I tell myself not to worry and I tell myself everything will be okay. This is my time to relax and be refreshed for the morning. I can worry during the day. So I count in my head 100 downwards and I say 100 in my head then take a deep breath in and then out. I do that with 99 and repeat, I tell myself to relax and take a deep breath in and out. I do that until I feel my mind wanders. Also you could imagine a nice place or somewhere you love. I hope this helps.