In order to prosper, you need to carry your emotions and put them to excellent usage. Professional athletes discuss this all the time, how nerves are GOOD as they show that this matters and this is what you desire. So, if you are exceptionally worried about taking the exam that is excellent if it is for the best reasons.
Nevertheless, you should never get in the exam room with a poor psychological mindset or with the feeling that you are going to stop working. I have informed trainees that if you stroll into the test room believing that you are going to fail, you may as well stroll right out and not lose your time.