abstract:A deep water blackout is a loss of consciousness caused by cerebral hypoxia on ascending from a deep freedive or breath-hold dive, typically of ten metres or more when the swimmer does not necessarily experience an urgent need to breathe and has no other obvious medical condition that might have caused it. Victims typically black out close to the surface, usually within the top three metres, sometimes even as they break surface and have often been seen to approach the surface without apparent distress only to sink away.
Of the manycauses of impairedconsciousness at depth, the conceptof "DeepWater Blackout" isdistinctfromthe moreobviouspossibilitiessuch ascopoisoningandMI.