Why Did I Have These Hallucinations?

Ok when I was like between 4 and 6 years I used to wake up like in the middle of the night and see a bunch of animals in my room like cats, birds, insects, iguanas. Literally any animal you can think of. I would tell my mom and her boyfriend about it but they wouldn't see it only me. And when they would turn on the light they would disappear. This would happen all the time and I was scared out of mind. So what was the cause of these hallucinations. BTW I'm 13 now.