I feed off stress like the bee off of nectar.
My advice: don't worry. Indugle in pleasure. Procrastinate at a reasonable pace (and not at the absolute bloody last minute), and you'll end up feelin' like a genius.
School is only temporary, but age will stay with you forever. Don't allow trivialities such as exams and what-not to make you grow old before your time, ARG. When consumed by adolescent angst, remember the immortal words of Oscar Wilde: "Life is too important to be taken seriously."