Having done quite a few sessions in the 'Ruddles Rocket' at Luffenham, I remember that we were told that you start to suffer from significant hypoxia when in an environment at 'half your accustomed atmospheric pressure'. Hence the chaps who live at higher levels can cope with even higher levels before becoming hypoxic than those of us who live at sea level. We were also given a whole load of rubbish about coping with jet lag - we told them the aircrew trick. Get drunk when you get to the hotel and wake up when the alarm call goes off!! They didn't like that one!!
Why the 'Ruddles Rocket'? Because we were always told to stay off the beer (the local beer in the mess was Ruddles County) and eat sensibly the night before the chamber run. Being aircrew - and the place being run by the arch-enemy (doctors), we always ignored their advice and went to Stamford for a curry and a gallon or two of Ruddles. The next day, the release of intestinal gas in the chamber was probably sufficient to propel a rocket to the moon.