original_query: What is shallow-water blackout?
query: What is shallow-water blackout?
answer: Shallow water blackout is a loss of consciousness due to cerebral hypoxia (lack of oxygen to the brain) that occurs in shallow water, often following hyperventilation before a breath-hold dive.  Hyperventilation lowers carbon dioxide levels, suppressing the urge to breathe and delaying the body's natural response to low oxygen. This can lead to a blackout without warning, often near the surface or even after surfacing.