you can probably return to that altitude without problems as long as you are properly acclimatized. The concentration of oxygen at sea level is about 21% and the barometric pressure averages 760 mmHg.

These considerations may include physical fitness, smoking habits, and overall health, which can affect a body's ability to cope with lower oxygen levels at altitude. Additionally, the FAA ...

“As we age, especially at altitude, we lose that blood oxygen level,” Formato said. “So for folks who maybe never really had altitude issues, those might start to get them in their 40s or 50s.