What is hyperventilation?

Hyperventilation is rapid, deep breathing in order to decrease the amount of carbon dioxide in the blood and increases oxygen levels.

It is especially dangerous to hyperventilate and then go underwater.

This is due to the low initial concentration of carbon dioxide in the blood; it would take a long time for carbon dioxide to build up to a level at which the decreased pH of blood would stimulate the respiratory centre to make you take a breath.

During this time your oxygen concentration may decrease to such a level that you become unconscious before the urge to take a breath occurs.

Then, when you are forced to breathe, you will take in water and drown while still unconscious. Many drowning deaths in Australia have been the direct results hyperventilation.