Consider the hours you are working and the type of work you do. Do you have an extremely early start to the day? Is your work strenuous?
Try not to eat beyond 7.30pm at night and don�t eat a big meal. If you have to eat later then go for slow release foods or food that breaks down easily; veg, rice, fish, fruit, muesli etc. Eat a big breakfast to give you a kick-start.
Do you drink much alcohol at weekends? Certain drinks can make you crash and burn. It varies depending on the individual but I�m a lightweight when I drink red wine all night!
Also, you mentioned that you fall asleep while watching DVD�s. Is this because you tend to sprawl on an armchair or sofa? If you�re too comfortable and warm then you will doze off.
If none of the above make any difference and you are prone to sleeping more than 8 hours a day then I would go and see your doctor as something else may be to blame.