What happens when you think more than you're accustomed to without properly stretching your brain first. Can result in serious brain pain and possibly permanent brain malfunction. Can be caused by overstudying, overthinking, overphilosophizing, and the chronic use of hallucinogens, which can decrease brain function and thus make an accidental sprain more likely.
Person: I've got my calculus class at 7am tomorrow...aauughh....
Friend: Oh yeah, I took that one last semester. I got a sprained brain from it, make sure you stretch before class.
Person: ...how...do you stretch your brain?
Friend: I dunno, but it gives you an interesting visual, doesn't it?