If i start an activity(studying,using pc,writing emails...)sometimes i can do this for hours without been able to stop myself until i fell asleep!why?

Obsessive compulsive: I understand your concern about not being able to stop yourself until you fall asleep, See a therapist for: Obsessions and Compulsion about various activities? Putting pressure on yourself, feeling obligated, and wanting to be perfectionistic? Feeling anxious or tense if tasks are not finished? Having difficulty in relaxing? and to learn coping skills to deal with stressors, Relaxation and Yoga.