Hey there, SalPal. I am much the same way with those stupid negative events. They pop into your head without warning and bring a black cloud with them.
Do you have an uplifting song that you could program your brain to "default" to? Its hard to just quit thinking of something -- but helpful if you have something positive to replace it with.
Best wishes, my friend.
PS: If nothing else works, there's always chococlate. Won't make anything go away, but I find it very comforting, lol!