I used to believe that you don't breathe when you're asleep. So, when my folks checked on me when I was supposed to be asleep, I would hold my breath.
A childhood belief about sleeping

others believed things like this
- I still hold my breath when I pass by cemetaries because it is impolite to breathe when other people can't.— Crystal
- If you hold your breath and make a wish under a highway tunnel it will come true....I still hold my breath :)— aj
- when i was a little kid. i used to think that when u hold ur breath ur heart stops.. LOL :P — Annonymus
- I used to think that a clown lived under my bed and tried to eat me while i was asleepAnon
- I used to think thats rats put those eye crusties there while I were asleep— Maria
- When I was a child i used to believe that if i did not fall asleep an elf would come for me Anon