I hate walls of text, so I'll just tell you what's worried me most recently. Developing a psychosis, primarily schizophrenia. I've had to deal with hypochondria for most of my life now, and it has periods of regression, but recently mental illness has been on my mind. I try not to let it affect my life too significantly, and just do what I can to satiate it, be aware of the symptoms (of the current obsession) then be rational about how I go about watching for them. In the early years my psychosomatic symptoms would be difficult to distinguish and develop rapidly but I've since become more pragmatic about what I consider a symptom, now I almost never see them anymore. It doesn't stop me being terrified I will become dissociative, paranoid or have hallucinations, or that I already am and don't realise it.
I get scared of deeply irrational things too, and take measures to then calm myself quickly doing or watching things that relax me. It tends to pass quickly.
Long term worries include, obviously, chronic degenerative illness, heights, spiders (but I'm working on it, I love spiders from a zoological perspective), rejection and syringes. I used to be afraid of loud noises, but as I got older I began to appreciate metal. Suffice to say that was soon after eradicated.