The urge to breathe doesn't come because one is low on air, but due to CO2 buildup in the blood. Humans have no physiological detectors for blood oxygen levels,

The urge to breathe doesn't come because one is low on air, but due to CO2 buildup in the blood. Humans have no physiological detectors for blood oxygen levels, they can only detect CO2. Normally CO2 buildup response is calibrated to be "early" in terms of oxygen, but the calibration can change (e.g. through hyperventilation) which can lead to blackouts and drowning since blood oxygen levels can drop below ones needed to keep brain "on" before CO2 buildup response even registers. Ignoring the urge to breathe is definitely not a smart thing to do unsupervised unless one wants an early, watery grave. Your response is misleading in that it implies "mental toughness" (utter bollocks) or a skill that some people have more than others. If Navy Seals (or anyone else) do this for real, you can bet your ass they do it under strict supervision, when training/competing (e.g. BUDS).