Making symptoms will surely be a challenge. It would have to depend on altitude firstly, but to make a creeping loss of consciousness is impossible unless our computers gradually injected carbon monoxide into the room.
For the purposes of a game, and to avoid possible lawsuits, it might be ok to just gradually dampen movement of the head and stick. This will be less noticeable during cruise when the inputs are more relaxed (but imagine being bounced at this point
). At some point the screen could go black, but by then there would be nothing you could do to wake up unless your plane was diving into thicker air. Whether or not you woke up before hitting the ground would also depend on many factors, but your chances are slim.