I've been told the best type of study break is one where you stop thinking. Can't stop thinking? Try making the right and left side of your brain work at the same time. Easiest way to do this (so I'm told, and I might be wrong) is to use your hand on the far side of your bodies' centre line.
For example, right hand holds left ear lobe while left hand holds nose. Now switch them so left had lets go of nose and grabs right ear lobe while right hand lets go of left ear lobe and grabs nose. You HAVE TO GET THIS RIGHT! No cheating and grabbing around blindly for something near your eye hoping it's your nose! Do it properly and slowly, then try to speed up the process. I'm told that working on doing this well stops you from thinking about anything else - you have to concentrate to get both sides of the brain working together.
But personally, I like to take a break by clicking the red dot. Trust me, it's mindless.