I'm not a professional programmer. As such, it's probably easier for me to be "hooked" into programming, than someone who has to do it for a living, and usually isn't working on projects s/he has chosen.

I find that I get into some project - whatever has caught my fancy - and spend a whole lot of time on it, often staying up late,and so on. Then I eventually finish, and spend some time recovering.

Which brings me to another point - when is a project "finished"? In the real world, it must be when you've met the various criteria for it as determined beforehand. In my case (and I suspect in others'), there really is no official "done" state. Once I accomplish my initial goal, there are always those little bits you want to throw in, the "creeping featurism". I'd say that I don't so much finish a project, as abandon it.