I've slept like that my whole life. Now I only pull the covers over my head on cold nights.
Two of my kids often have the covers over their heads when I go in to wake them up. I don't think they intentionally pull them up that high (they don't fall asleep like that), but they just move around throughout the night and often wind up down inside the blankets. I would check on them more often when they were little and pull the blanket down if necessary, but now I don't worry about it anymore... of course until I read this thread.