Why can't I sleep

Why can't I sleep. Is it that I have a problem with my body or is it that I need to watch the next season of glee on netflix? Well I close my eyes but I just can't  fall asleep. I think I know why I can sleep it's because I'm worried about my F in this class so I'm doing this? But Nelson if you see me tomarrow and I look tired I think its one of these reasons.