In psychology this is known as “rumination.” There might be other terms, but that is one. It is a common thing for one negative thought to lead to another.
Rumination is a habit under your voluntary control and you can stop it, with effort (and prayer).
I recommend reading Jewish sources on positive thinking and how to avoid negative thoughts. If you google “Don’t dwell on bad thoughts or desires at all” and “Search for your good points in order to make yourself happy,” you will find chapters from Likutei Eitzos, which contain a lot of chassidic teachings on this and similar topics.
I’m sure there is a lot of good material written by psychologists for the general public on this topic, too.
Hatlzacha! Lots of people deal with similar issues, but many have overcome them through education, effort and prayer. You can do it too.