I had done the old traditional training in a pressure chamber at Beale AFB 7 years prior. It was worthwhile, but quite frankly it was a pain for the average pilot to go there and spend close to a full day for the training where the relevant part is really only 20 or 30mn.
When I found out that the FAA came up with a new training where instead of needing a bulky pressure chamber, they could just setup a tent, remove oxygen and pump in nitrogen instead until oxygen percentage was down to 8% or so, I found the idea very cool. It gives your lungs the same partial pressure of O2 than at 25,000ft or so, but without worrying about reduced pressure of air, and getting the bends.
So, I went to do it again, and the effects of O2 deprivation were similar for me: I don't feel happy like some do (which is bad, that's how you die), I start feeling not good while otherwise remaining functional. My brain slows down, but I can still do one task at a time if I really focus on it, and this second time, I didn't turn quite white like the first time, but I got very hot and sweaty. I was literally wet under my clothes and my body continued that reaction for another 5mn or so after I was back to normal air.
I tried my best to write down my O2 saturation during the exercise. It never dropped into the 60's which is where some people got, but I still was quite impaired in the 70's and couldn't have stayed at that saturation for much longer.
What's interesting is how my heart rate went up to compensate for the low oxygen, and then it seems to have given up. Not good...
I have a coworker who took a couple of pictures for me, and this time I filmed the event so that I could later see the time distortion (what feels like 1mn to you because you've slowed down, is actually 5mn of real time):
an instructor was giving us commands
I looked focussed on whatever I was doing, and not too white this time :)
And here is a short video of the session showing how we deteriorated over those few minutes:
