Immersion is forgetting that you're playing a game, and it's different for everyone.
This.
Not seeing time fly by doesn't mean the game it,s immersive, just that you enjoy it.
I mean time past fast while playing say TF2, but it's not immersive at all.
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http://img.imgcake.com/cosplaygifer.gif
http://en.wikipedia.org/wiki/TORtanic