... you start to get the craziest dreams like walking around Runescape with the white mushrooms from Kingdom Hearts following you around.
... you start to call your family members by the videogame characters they resemble (or are on your mind).
... instead of worrying if your gaming time will cut into your academics, you're worried your academics will cut into your gaming time. (Honestly, that's just bad).
... the only conversations you can have with people are videogame related because you are so out of touch with the real world (Tsunami what? When did this happen? Yo! Did you see the new patch for [game]?).
... everyday life becomes a scene in a videogame, perferrably multiple ones. (Oh dude, you're girlfriend left you for that football player? That's just like in [game] don't worry, you'll eventually get to hack them both into pieces.)
... you feel even the most senseless games have educational value. (Steal is made with two coal and a iron ore! OH! I know what to do! I have a lvl # first aid in WoW!)
I'm sure I could go on with real life examples, not all of them my doing (I was aware of the tsunami, but I think that's the only one I'm not guilty of at least once....). Beware, these things really are addicting!