https://en.wikipedia.org/wiki/Freediving_blackout#Shallow_water_blackout https://en.wikipedia.org/wiki/Freediving_blackout#Shallow_wa... Apparently hyperventil

https://en.wikipedia.org/wiki/Freediving_blackout#Shallow_water_blackout https://en.wikipedia.org/wiki/Freediving_blackout#Shallow_wa... Apparently hyperventilation does not increase your oxygen levels, but instead reduces the amount of CO2 in your blod, which suppresses your suffocation reflexes.