McNabb was gassed in a Super Bowl, only he didn't pull himself out of the game. He just let a ton of time roll off the clock.
I have to think a lot has to do with not breathing properly. Sometimes we hold our breath when performing tasks and don't realize it.
A professional athlete, a starting QB no less, pulling themselves out of game for being winded... I have to believe it was necessary.
It was his honesty that was the mistake. He should have said he was feeling light headed.