One should probably keep the book & pen ready for such contingencies. You may run the risk of being called a "schol" by your unappreciative classmates/co-inmates, but at least you will have something to do while seemingly making notes. You will find your sketching, poetic, orthographical skills improve. Even your ability to keep the straight face while guffawing behing those set jaws. I remember writing a few poems in Systems Programming classes (the ones I attended, not the ones I take ;-) ) and composing an alternative quiz in Multimedia Techniques. More of those and I'd have been able to take a better career decision.
Ishtori: (My cousin swears he did this)
My cousin is a Ph.D in Dentistry, something that doesn't happen everyday apparently. As a working student, he had to take a class some day. It had the usual compliment(sic) of sleeping students. At the end of this lecture, he apparently woke Rip V. W. and thanked him for not snoring and hence disturbing the others who were soundly off to the land of nod-nod.
Not as bad as the story in which there was one guy who dozed off in the middle of the lecture... which he himself was conducting. Kuch bhi kya!