Not sure if the same but college math classes threw me into intense drowsiness, almost narcolepsia, I couldn't hold my head just by looking at the board. Coffee intake did nothing. Just moving away from these classes brought me back.
I can't help but think that it means "you're in the wrong place."
For example, in my high school AP Calc class, I often couldn't stay awake because I picked up on the concepts very quickly whereas my peers did not and I would quickly get very bored when being lectured on the same topics day after day. Contrast that with the amount of books on Mathematics I currently own, that my favorite language is Haskell and that I currently am employed writing software.
It was almost as if my body had developed a heuristic for how useful today's class was going to be and reacted accordingly. The same sort of thing happened through college (Psych, Business, etc) whereas I was known to read psychology textbooks for fun when I was very young.