Highly elevated CO2 levels can produce panic attacks, and the body's ventilation is sensitively controlled by CO2 levels.

“Now under normal circumstances your oxygen levels are fine and unless you go to altitude they don't really change very much but your CO2 levels can change quite a bit with even a relatively small change in your overall breathing that's going to change your pH level. ... we know that highly elevated levels of CO2 can produce panic attacks. Your body is so sensitive the control of breathing like how much you breathe per minute is determined in a very sensitive way by the CO2 level.”