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.

Many individuals, especially those not accustomed to high elevations, may find it challenging to adapt to the environment due to lower oxygen levels. This could result in altitude sickness ...

Physiologically, a large portion of the negative effect of altitude on exercise performance can be traced to limitations of oxygen diffusion, either at the level of the alveoli or the muscle ...