look up "freud" or "psychoanalysis" and "defense mechanisms"
I found a link here
http://en.wikipedia.org/wiki/Defense_mechanisms
I think procrastination is one way my defense mechanisms work. sometimes I get stressed out when I have to write an essay because I think it's too difficult (actually I'm good at writing, so these thoughts are wrong) and in denial of the stress and regression to old bad habits, I procrastinate to relieve the stress, denying that I have to do the assignment I guess. Also I was usually too ashamed to hand it in late. That didn't help. :P
It's probably more complicated than that, but that's my general theory... although maybe it doesn't apply to other people... but it seems like procrastination is a way defense mechanisms work for a lot of people.
So you have to realize that procrastination is something your unconscious mind is making you do in order to relieve the stress of the upcoming exams or essay due date (which in the long term, is the worst stress reliever because you become more stressed the more you procrastinate!) Read more about defense mechanisms so you can kind of recognize them. and find other ways of relieving stress, skiing, stuff like that, also if you start the task at hand you'll find it's not as ominous as you thought.