Yeah, that is definitely a danger, over-stretching. I injured my knees overdoing jogging in college (speaking of overdoing things) and so they are very sensitive to over-stretching—and very sensitive to not stretching at all, so it's a balancing act.

haha going back to sleep. I can't say I have that problem with yoga, but if I am tired in the least my meditation sessions can quickly result in sleep. Actually, my reading does too. Hmm... anything that involves sitting does, come to think of it.