Passion vs obsession

When does passion become obsession? I've always been interested in art. I used to envision working for Disney. I used to strive towards becoming a cartoonist, but I never had the overwhelming desire to excel at anything until I found computer graphics. The more I learn, the more I develop my skills, the stronger my desire to learn and develop becomes. This may be passion, this may be on the brink of obsession. But last night I was dreaming Of a current project, and actually made progress in my dream that I used in the waking world. Now I don't know if this qualifies as obsession, but I do know I need to lay of the pepperoni and swiss before bed.