H.B.
My son is only three, but this happens with him, too. I don't think he really wakes up, he will sit up and just cry and cry. When I talk to him he kind of looks at me crazy and pushes me away, if I mess with him too much he just gets more upset. I think he's just really sleepy and confused. I've heard that sometimes kids release emotions when they're sleeping. I like to think that's the problem and that he's just so happy when he's awake that he doesn't get a chance to get his cries out. :)