I have read posts by several carers for people living with dementia which mention that they, the carers, have an ever-present fear of getting dementia. Usually the simplest common memory lapse will activate this fear.
Sometimes, when they have parents or siblings with dementia they worry about the possible genetic links, but often it's their knowledge of how common dementia is that causes the worry.
I don't have this particular worry - despite the fact that my mum had Alzheimer's - though I have, and have always had, a degree of hypochondria and, at a few points in my life, I've been convinced that I was dying. Obviously, I was mistaken (except that we're all dying)!
Now that my life is largely involved with keeping someone I love alive, I worry about my own health in a different way. I'm concerned not just about my own future, but also the effect any health problem may have on my wife.
Also, of course, as one gets old, and more and more friends and acquaintances fall by the wayside, real health issues, whether serious or trivial, tend to increase.
It all comes down to the well-worn cliche about taking each day as it comes. It's not easy, but it makes sense.