I felt like this study was worth noting all itself:
http://news.yahoo.com/s/space/20060827/sc_space/brightideasunlightcurbsafternoondrowsiness
Also, taking a 20 minute cat nap can help rejuvenate you, drinking water, changing your surroundings... there are all sorts of ways to avoid falling asleep...
unfortunately, none of these work for when you have a monotone professor who drones on about world economies at 8am. Sorry CMU kids.