There are only some situations where they should care - like if you have to do some kind of active work. If you're just there to take notes, I don't see why they should care (unless you are snoring loudly). Then again, I never understand people who go to lecture just to fall asleep? What's the point? You'll get a more refreshing nap in your own bed - and then you can get the notes from someone and learn the material after you have had good rest. This way you get poor rest and still don't get the material until later (if ever) anyways.