Hyperventilation and carbon dioxide loss

Hyperventilating isn't simply breathing fast, even though the name suggests it. Hyperventilation is defined by what happens to carbon dioxide, the waste gas your cells produce all the time. It's happening when the air moving in and out of the alveoli, the little sacs in the lung where gases are traded with the blood, carries that gas away faster than the tissues can make it.

Picture a sink with the faucet running and the drain open: as long as the same amount goes out as comes in, the water level stays put. Breathing deeper or more often is like opening the drain a little wider, which is why it isn't always enough. Only when you truly remove more than you produce does the level drop. Low carbon dioxide in the blood has a name, hypocapnia, and if the pH also rises, the measure of how acidic the blood is, then it's called respiratory alkalosis.