One of these science of studying articles pops up pretty regularly. Here's a new one via NPR which encourages an on/off study pattern (instead of on/on/on/on): Studying? Take A Break and Embrace Your Distractions. From the article:
Distraction is one of those things everybody is worried about— certainly every parent, with the iPhones and people jumping on Facebook and so on. And of course if you're spending your entire time tooling around on Facebook, you're not studying, so that's a problem.
However, there's a whole bunch of science looking at problem-solving. In problem-solving, when you get stuck, you've run out of ideas, distraction is really your best friend. You need to stand up, let it go — walk around the block, go to the cafe, drink a beer, whatever it is— and that is really your best shot at loosening the gears a little bit and allowing yourself to take a different and more creative approach to the problem.
If answering exam vignettes isn't "problem-solving," I don't know what is. So, set down the practice tests, step away, catch a breath. Just make sure you get back to studying sooner than later. Happy studying. Good luck on the exam!