Why should divers avoid excessive hyperventilation when freediving?

Avoiding excessive hyperventilation when freediving is crucial primarily to prevent shallow water blackout. Hyperventilation can decrease the carbon dioxide levels in the blood, which may give a false sense of safety regarding oxygen levels. This can lead divers to hold their breath for longer than their oxygen supply allows, increasing the risk of losing consciousness underwater due to insufficient oxygen. The brain is sensitive to oxygen deprivation, and if divers do not recognize their limits because of the altered perception created by hyperventilation, they can face dangerous situations. Therefore, maintaining a proper balance of carbon dioxide and oxygen is vital for safety during freediving.