This is when you're desperately needing some head, but your girl's asleep. Therefore, you sneak into the room and stick your dick in her mouth while she's sleeping. By instinct, she'll probaby start sucking your dick while sleeping, giving this action the name "Sleepy Head"
Friend 1- Man, the other night my girl was asleep and I really needed some head.
Friend 2- I guess that left you to use your right hand for the night,
Friend 1- Nah man. I just stuck it in her mouth and she gave me some sleepy head.