Yeah, it definately needs to be checked out. But aren't they teens? I mean, teens can fall asleep when you are talking to them.
I was thinking in terms of sleep deprived teens. I have not been able to count the number of articles I have run across about schools starting so early and teens inner clock running so late instead. Thus they are not ready to sleep when they would have to go to bed to get the recommended number of hours given the time they have to get up in the morning!