What are you doing BEFORE the test, and during the break BETWEEN sections? The best thing you can do:
Before the test:
--Make sure you get a good *weeks* sleep before the test.
--Make sure you are ACTIVE (regular exercise is great for energy).
--Make sure you are EATING WELL.
--Practice MINDFULNESS and MEDITATION.
--Do long question sets.
--Take practice tests! The only thing that 'gets better' *during* a practice test is endurance (other improvements come from *reviewing* practice tests).
In the break between sessions:
--Get up, move around, stretch, get blood flowing.
--Do some deep breathing/mindfulness focus.
--Get some SUGAR in your blood (studies show blood sugar levels drop significantly when 'thinking' hard, which the test demands. This drop makes one tired and makes their reasoning worse. I brought a brownie for the interim when I took the test).
--If you're a caffeine slug like I am, maybe a little coffee (I put a cup of coffee in my locker, along with my brownie).
I have also heard teachers recommend, somewhere along the halfway point of the second section, finding a question that makes you wanna die, and instead of skipping the question immediately, just rest for a moment. Take some deep breaths, use the time to rejuvenate for the last half of the test.
If that makes you freak out, you're not thinking about how the test is scored! You think you should try to get every question right. You shouldn't, and you won't!