Do you remember having any unrealistic fears as a child? I had some...
1. I believed that if I stopped focusing on reality, it would fade away into nothing. So I was especially scared that I would forget about breathable air and/or gravity when I fell asleep. Or even wake up in a random, possibly dangerous area if I didn't remember anything about where I fell asleep.
2. I was afraid to walk on grass or dirt.
3. I would become afraid of and avoid specific empty areas of space for no apparent reason. I would start to believe for some reason that something dangerous was there even though I couldn't see it, and that it would harm me if I got too close, but it wouldn't affect other people.