I know exactly what you mean. It will pass in a few days.

What I do when I get a thought I don't want to have - I snap myself out of it and force myself to recall something pleasant. A cool movie, making a plan for next day, daydream about something. Then I keep that thought in my head until it takes off on its own.

On occasion, I tell myslef "That's stupid, why would you be doing that to yourself. Stop it". Sometimes it works. Good luck