Pkitty, I've had experience with altitude-caused hypoxia. I was at NASA, preparing to fly in the KC-135 "vomit comet," and they put us in a decompression chamber to simulate air at 30,000 feet. We got to breathe through jet fighter oxygen masks first to make sure our blood was nicely oxygenated, but then we took them off. 10,000 feet was no trouble at all, but when they lowered the atmosphere to the equivalent of 20,000 feet we started to get a little woozy.
They gave us a little worksheet with a crossword, a connect the dots game, and a questionaire asking us to name who the last ten presidents were, what our name was, and so on. I got a little past halfway before one of the NASA guys started shouting for me to put my oxygen mask on. I'd apparently been staring off blindly for half a minute, not even realizing that my brain wasn't working anymore.
I can also tell you a lot about freefall and motion sickness, if you want. Don't look quickly from left to right while in free fall. It won't end well.