I've always been afraid that someday, because of some heavy trauma, I'd lose my sanity forever. Schizophrenia is very scary indeed. Or dementia, Alzheimer's, ALS, etc.
I'm somewhat of a hypochondriac, honestly. I'm also horrified of needles, but I've gotten somewhat used to them in my early adult years.

I'm also scared of getting stabbed. Shot too, of course but stabbing terrifies me.. the concept of the sharp, cold knife entering my body and piercing some vital organ is just shudder-worthy. The bullet is a lot more harmful I know, but maybe because I'm so familiar with firearms knifes scare me more?
E.g. I'd be more scared of somebody putting a knife in my throat (which I've had) instead of a gun behind my back, simply because in the latter I doubt he'd pull the trigger while with a knife it's silent and he'd be more likely to at least injure me if he wanted to (out of spite or during a mugging) and less scared of anybody hearing it.

In a way I'm also a little scared of getting married (and divorced) especially with the crazy statistics in the last couple of decades its become somewhat of a joke. Since my father owns a few real estate properties (which he's worked A LOT for) and I'm an only child, I'd be horrified of marrying the wrong person and losing half of them to some gold-digger. Of course there's the prenup but those are always trouble.