My brain goes on vacation a week before finals EVERY TIME, how do I stop this?

I don't know what happening, but I swear my IQ drops 20 points right before finals. Questions that I'd normally not sweat, I suddenly can't remember how to do and I'm messing up. This happens every term and I normally do well enough throughout the semester that I can survive the hit, but I'd rather not need to. I don't know what to do about it, has anyone else found a way around this? Maybe I don't actually know how to study/review or something.