Obsession vs Passion

How blurred can the line between passion and obsession get? There are some video games that I can really get into. So far that they seem to find their way into my dreams, putting me into states of playing them, being in them and waking up, thinking about them. Nothing else. Last night, for what seemed like endless hours, I was either talking to different aliens races in Mass Effect 2, or I was awake for a few minutes, thinking about it. Nothing about school or general life problems arose, only that game.

I realize this usually happens with a select few games, and only when I play them for really long, consistent periods of time; such as World of Warcraft, Team Fortress 2 or Thief. Also, sleep deprivation and general stress seem to play a role. When I have these dreams, they're very intense and I feel great in the morning, despite waking up at random times and falling back asleep.

This is when I ask the question: Am I just really passionate about the games I play? Or am I obsessed, nearing addiction? Or is it not so black and white as I put it? Perhaps there's a middle ground I'm at, which seems to give me the most satisfaction?