Stress then Relief?

I study for days before and hours leading up to a test.  Then when I see that test before my eyes, my anxiety goes up and beyond.  I start to panic and I cannot catch my breath.  However, I start with number one and by the end of the exam I realized that I did one awesome job.

Now, how can I go from believing I am a failure, I am stupid, and that I did not prepare enough for the test.  To going to Yes! A+ I do not understand.  I am intentionally ridding myself of my own dignity, judging my intellifence and humanity to the people around me and the inanimate object (the test).  Why do I do this to myself?  Why does anyone self-tortue themselves?  I do not know if a good grade is worth the pain I put myself through before the test. 

This world is one crazy place, and we are making it crazier for ourselves with every step and word we take.