Constant stress and worst-case thinking.

I have been experiencing constant stress and overthinking for quite some time. Almost every day, a small issue or uncertainty becomes extremely stressful in my mind. My thoughts follow a chain: I think about what could go wrong, then its consequences, and eventually reach a worst-case scenario. For example, a concern about walking a lot while travelling became: what if I cannot keep up, others may not want to adjust, I may have to travel separately, it may become expensive, and eventually I feel incapable, dumb, and unable to manage life. This happens with different situations. Even when there is a lot to be happy and grateful about, my mind focuses on small potential problems. I feel constantly under some form of stress, and my mind rarely feels at ease. Sometimes I cry and feel overwhelmed or helpless. I want to understand why this keeps happening and how to manage it better.