I always wait until the last minute to do huge assignments

First, I'm not a doctor, so don't take me too seriously. However, I am an ADD'er, and what you describe coincides precisely with ADD symptoms. People with ADD can ruin their lives by procrastinating/waiting til the very last minute to hurry and get it done. What happens to you when you do this? Stimulation! Stimulation is what ADD people need and they get it, especially if they are untreated, by the rush and urgency that comes along with the behaviors described. If your treated, however, medication, if needed, will level out the need for stimulation by giving you stimulation. One word of advice: go to the best psychiatrist that you can afford who specializes in ADD. Many others seem to think that you outgrow it like a pair of old shoes. Insane! Good luck.