Cause of childhood hallucinations?

I used to see and hear very strange things. Like faces, hands, flickers of movement. Voices. Whispering. Laughter. It stopped when I was 11, perhaps? Haven't had a single recurrence since, but it even bothered me when I was a toddler. I'd cry about it. No idea what caused it, does anyone here know? Just FYI I'm nearly 18 now.