I mean, the only thing I can think of would be an anxiety disorder. Anxiety can create thoughts that aren't not even logical, and can be based on anything. Personally, I have anxiety about dying of a heart attack. I get chest discomforts all the time due to it, and used to have attacks with heart palpitations and sweats before going on meds (which I rarely take anymore). If you get anxiety from those thoughts and get anxiety attack symptoms, then it is most like an anxiety disorder. But if you're just kinda sitting there worrying about having a mental illness, then I would just call it intrusive thoughts. Intrusive thoughts are unwanted thoughts, and something you just gotta deal with until it goes away. You can seek professional help if it is really bad.