Just before I fall asleep I hear voices?

First off I'm 15 and I don't think I'm insane it's just right before I fall asleep I either hear someone screaming something like "get down" or the sound of leaves being blown in the wind I also hear a very disturbing creepy voice say "Satan" an then I usually jump or twitch which wakes me up from being half asleep. Also lately I've been having sleeping issues. I often go to bed at 12 and don't fall asleep until 4 and I don't wake up until about 1 or 2. What is this? Am I crazy?