I've played a bunch of Guitar Hero and Rock Band, and I've noticed a few things.
1) That weird vertigoey feeling you get when you've been playing for a while (say, a week or two, straight) and you look away from the screen. Everything seems to be moving away from you--almost like going into a wormhole or something.
2) Self-consciousness about rocking too hard. Sure, you want to do well, but at what point do you cross the line from keeping up with the notes to Pete Townshend windmills at the end of your song?
3) That brief feeling of apprehension you get when you hear a song from the game out in the real world. For just a second, your hands tense up, trying to make sure your fingers are in the right place.
Or maybe it's just me.