3 words
Ulnar nerver entrapment. Google it. Your Ulnar nerver is actually your funny bone. You know when you hit it how it feels. When you sleep with your elbow bent it swells up a bit and you get the numbing feeling.
Position is the right answer from the others, but it is kinda hard to control when you sleep. Try popping an asprin or anti inflammatory before you sleep.
Good Luck.
