Over confident?

Since when is being confident bad?
Well it appears that whenever I take a test I feel an exuberant amount of confidence. I even double check everything. I then pick up my belongings and happily turn my test in. A smile will then dance across my face as I prance down the heavenly stairs of the testing center. At this point in time I am so confident that I just aced that test. But don't worry, this confidence is easily and rapidly deflated. The once exuberant Julie is now wondering if my memory has failed me yet again.
"Maybe that number is not mine?" (too bad short term memory loss doesn't constitute of losing years)
"Maybe the testing center messed up while correcting my test?"
"Maybe the lies of the high school teachers are truths" ("mark anywhere out of that circle and the computer will pick it up and mark it WRONG!! Even if it is the slightest mark".....okay maybe my paranoid self made up that second sentence, but HONESTLY!)?
These insecure thoughts race across my mind and inflict me with the horrible disease of self-doubt.
Are tests made to frustrate the confidence of students? Students rely so much on the score they receive. Personally, I project my final grade from every test I take. This is due to the fact that NO other assignments have as great of an impact on the final grade in the class. Thus, I study my butt off for (most) tests. And when several hours of dutiful studying has taken place, an individual should do well on a test.
Is it overconfidence from all of that studying and/or the right that students believe they have after studying that cause students to do worse on a test? I don't even know. I could probably create some conspiracy theory. Yet that would not do me justice from the emotional damage that was done. All I know is that I was depraved of my confidence tonight.