heh, you should've seen my psychology class today. We had to read a topic on 'arousal and performance'
It stated that if you were not aroused enough, your level of performance would not be good, but if you were over aroused, your level of performance would also not be good as you would be too jittery and excitable. A medium level of arousal promotes optimal performance in most things.
...and they seriously put that in a textbook for teenagers. Maybe they were trying to give the teacher an opportunity to cure us of our immaturity. Didn't work.