In high school, exam week was quite honestly a joke. I never really got worked up over exams because there was ALWAYS a ridiculous curve. In extreme cases, tests that originally earned an F would be curved to a high B. In college, that is obviously not the case.
From my experience, it is pretty normal to have classes be 100% exam-based. This means that my entire grade for the course comes from two midterms and a final. I think this is absolutely crazy.
Sometimes, tests are just too hard. I can study for a week straight and still manage to not get the grade I need on exams. Professors try to make these tests as hard as possible. Just because I don't do well on an exam, doesn't mean I don't understand the material. It is possible that the professor simply did make it too hard.
I'm currently in a marketing course and we just had a midterm last week. When I was leaving the exam, I remember being so mad because I knew that some of the questions had multiple right answers. I was right. Luckily, this professor takes appeals on questions and I managed to get some points back. Unfortunately, not all professors are like this.
I know that constant homework assignments and weekly quizzes can be annoying, but they are great for boosting grades. Some students have really bad test anxiety and can fail a test even if they know the material. By allowing a percentage of our grade to be made up of "lower-stress" assignments, professors are giving students with test anxiety a chance to succeed.
I don't think exams should be completely abandoned in the classroom. But, I also don't think they should make up your entire grade.
Midterms are stressful, finals are stressful, college is stressful. I am guilty of not sleeping, eating or socializing all because of an upcoming exam. We just all need to relax a little bit. It will all be alright. A bad exam grade is not the end of the world.