You have that terrible thought that is hammering away in your mind. Here is what you may want to try doing. Have a good thought that you switch too, just something that makes you feel happy. And when ever that bad thought just starts to creep back into mind then all you need to do is to just switch to that positive thought. And when the bad thought comes back than just gently switch back to the much more positve frame of mind than you were before. Maybe this might work.