When I study for the exams, I have this habit of getting up every 15 minutes or so, grabbing my white mug from my desk and walking down the corridor to go get myself water. Then I just stand there, and l kind of lose myself a bit and stare into space, while I drink. Then I go back to whatever I was doing, and go fetch myself some water again after 15 minutes. 

I do have a tumbler to save myself the trouble of standing up but.. ugh it has become a habit.