A couple of guys regularly fell asleep in one of my classes last semester. The professor was incredibly intelligent and had worked as a contracts lawyer in Europe, but . . . he was as blind as a bat. Needless to say, people took advantage.
One guy would fall asleep in the most obvious ways. His head would tilt back, and then he would jerk awake. Then he would go back to sleep. I sometimes watched as he went through this process, because his eyes would start to sag really badly and you knew he was out.
Another guy fell asleep with his hand on the "n" key of his keyboard. He typed nnnnnnnnnnnnnnnnnnnnn for around fifteen pages in Word before someone woke him up. Someone also threw a paper clip at him.
Falling asleep in class is bad.