Students don't usually "freak" out in the middle of the test, the problem more often than not occurs in Biology which is the first section. If you are not fully prepared and those first questions come at you and you can not answer them it can cause panic to set in. If you are fully prepared there should not be a problem. But during the test always remember to breathe, when nervous most of us have a tendency to shallow breath which heightens stress.
What day are you taking your DAT?
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Nancy