Instapaper your worries. That is, save them for later. By the time you come back to them, they'll only be important if they're still on your mind.
Anxiety is a trigger, one that works to benefit you. You'll continue to think about the exam if you do nothing about it. Studying builds up your confidence and reduces your nervousness. Nevertheless, some worries are like inbox zero are excessive. Overthinking can often lead to overdoing, which falsely prioritizes unimportant things like answering every email.
The longer you wait to tackle apprehension, the more anxious you'll get. In fact, the feeling of procrastination is often worse than doing the actual work. Everything fades away once you get started, paving the way for a clearer future ahead.