It is called "anticipatory anxiety"... We tend to worsen thing before they happen, and feel less stressed when it actually takes place and after...
People in a survey, about being in exams/job interviews/etc, had to put a punctuation (between 1 to 10, 1 nothing nervous and 10 freaked out) in the stress felt "before, during and after" the situation which made them nervous... The results were that people before the events felt nervous from 8 to 10 before the events, 5 to 6 in the meanwhile and 1 to 3 when it ended...

Anticipatory anxiety ruins us all!