Have you heard of Yerkes–Dodson Law? It states that performance and stress (arousal) are directly related.

Arousal levels help us to focus our attention and motivation on the task at hand, but only until an optimum point – when levels of arousal become too high, performance decreases.

If your anxiety level is at an optimum balance, then you’ll find yourself performing better by remembering the right answers to the question (on the exam, for example) or by controlling mind flow during a meeting presentation.

However, if you’re overly anxious you’ll feel nervous instead, which would then hamper your ability to remember the information you specifically learned/prepared.  

The optimal level of arousal depends on task complexity. At a track meet, it is almost impossible for sprinters to get too aroused for a race. The task is direct and uncomplicated: Run as fast as you can for a short distance. On the other hand, a basketball player making a game-deciding free throw faces a more sensitive and complex task.

How does this work in your case?