So my comprehensive exams (aka qualifying exams) are coming up, and I've been studying my rear off to be ready for them. Anyway, today I switched from character theory to functional analysis, and came to the sudden and horrifying realization that my brain has stopped working. Essentially, I have all my study materials in front of me, I just can't seem to put my nose into my books. My brain is just so exhausted from studying for so long that I can't seem to focus long enough to process any information. What it comes down to is that I need a way to refresh my brain. Does anybody have any tips on how I can do this? I'm done to only 3 more weeks of studying, so hopefully nothing too drastic.