Try having a pleasant mental image you can quickly contemplate as soon as you start to think about the bad event.

Note that this can backfire, since the pleasant image may become mentally linked to the bad event and thus develop negative associations. (I still think it's worth trying, but choose a pleasant image you can stand to lose.)

If the bad event involved someone else doing something bad to you, forgive them

Easier said than done, of course.

I have this problem and do intermittent fasting. I never before thought there might be a causal connection.

Interestingly, I also have this and similar problems and don't eat very much.