In 2005 I took the PMP exam. It was four hours long. I was really worried about the length of it and was afraid to get tired and loose focus. My experienced friends told me that I was allowed to take breaks. So, I carefully planned them: when would I take them, what would I do in them. I took large coffee to exam room, in break I went to wash room relieve myself (even though I don't need it) washed my face, ate some snacks (I even put some thinking in choosing snacks, so that I would get the maximum energy for my exam and don't bother my digestive and other systems too much).
I didn't think too much about the exam during the break but everything I was doing in the break was to rejuvenate myself for rest of the exam.
Indeed it worked and I was fully focused till the last minute. I passed the exam.
Moral of the story: if you haven't got it by now this post is not for you, sorry to take your time.