As a kid, mysterious lights in the dark, like cat's eyes in a dark room (except not because i've always loved cats, more lights that are like that but i didn't know what was making them).

As an adult... prolly nuclear war.
I'll be honest, the one thing I truly fear is the day my body becomes so weak I can't even support myself. that is what I fear.
Personally, I fear a lot of things.
To name a few:
Dying alone
Horror games that have a lot of tension because it causes my anxiety to spike
A thing that happened years ago happening again
Becoming a different person from what I am used to
and actually, I fear how much hypnosis can do (as someone earlier said) because as erotic as it can be/is, I always find myself thinking about what would happen if it was used to change someone's base nature.

(Also somewhat late to this, as it was a halloween thing, sorry.)