Not an actual fear of something that would happen, but there was a nightmare I had when I was a young Christian boy (around 5-7 years old) that terrified me.
I dreamt that I got separated from my mother while we went shopping, got lured into hell by a demon, and placed into a contraption that turned me into Satan's second-in-command. I remember growing horns and doing an evil laugh the moment before I woke up.
I was borderline traumatized. I talked to my preacher father about it, but said I saw it happen to someone else, as I didn't want him to imagine that happening to his son. But now, as a middle-aged queer atheist, I embrace my role as Satan's loyal devotee, even if I don't understand what I did to move up the ranks so quickly.