Oh thats adorable! Penny does that too, sleeps half in her bed. She usually does it though because she is a pack rat and puts so many toys in her bed that she can't fit her whole self in it! It's really cute though.
Our boys sleep on their heads. Well, I mean they are 1/3 off the couch and the 2/3 left is laying over the side of the couch or bed, whatever. I'd think they'd get a headache with all the blood rushing to their heads, but they get upset if you try to move them to what I think is a more comfortable position.