When I was in college, I had this Econ professor who was a drone, and he always put up his lectures online. So when I missed class, id go over the webcasts of his lesson, and every single time by the 5th minute I would be knocked the fuck out. I quickly learned that this shit was stronger than NyQuil. Granted this may subconsciously make you always fall asleep in lectures if you do it often, but I saved some lectures just so I could fall asleep. So yeah download some casts of your most boring professors.
Nowadays some whiskey and indica will do the trick.