How to overcome anxiety after an exam?

So i felt that i didnt do sufficiently well on an english exam i wrote because in the morning my mind was in in ruins and while writing it i felt nervous, thus my conclusion was rushed. basically i made a statement, 'nuanced' a quote and explained how it led me to that conclusion. Intro was meh and the last sentence of each paragraph somewhat summarized the content of each paragraph. :S How do people fail English exams?