Ok, I have one that is really specific and pretty strange. You know those small, artificial ponds that sometimes people have in gardens, with goldfish, lily pads, statues around it,etc? For some reason the idea of the bottom of those things freaked me out. The black tarp made it mysterious, I felt like I had no way of telling how deep it really was, so I imagined it went on forever, and it made me feel claustrophobia.
Another thing that freaked me out was the idea of transforming into something else, like a monster or an animal or something randomly. It wasn't the transformation itself that scared me, it was the idea of having to explain to your family or friends what had happened, and them being confused and bewildered and gawking at you. I always hated any movie or tv show that had any plot like that at all.
And in first grade whenever I looked out my window at night and saw our neighbors tree, I imagined that certain branches were monkeys that would crawl through my window if I fell asleep. I probably got that from Caps for Sale haha
Edit: ooh I thought of another one. Certain color combinations and patterns freaked me out for no reason whatsoever. Like warm-colored flowers on a black background. To this day I won't wear anything with that pattern on it. I didn't have a rationalization for that back then either.
And then I had some fears that were completely rational, such as the fear of thomas the tank engine. Seriously that is some uncanny valley shit right there