<unk> , breath-hold<unk>  or apnea<unk>  is a class of hypoxic<unk> , a loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold (freedive or dynamic apnea) dive, when the swimmer does not necessarily experience an urgent need to breathe and has no other obvious medical condition that might have caused it. It can be provoked by hyperventilating just before a dive, or as a consequence of the pressure reduction on ascent, or a combination of these. Victims are often established practitioners of breath-hold diving, are fit, strong swimmers and have not experienced problems before.<unk>  may also be referred to as a syncope or fainting. Divers and swimmers who<unk>  or grey out underwater during a dive will usually drown unless rescued and resuscitated within a short time.<unk>  has a high fatality rate, and mostly involves males younger than 40 years, but is generally avoidable. Risk cannot be quantified, but is clearly increased by any level of hyperventilation.<unk>  can occur on any dive profile: at constant depth, on an ascent from depth, or at the surface following ascent from depth and may be described by a number of terms depending on the dive profile and depth at which consciousness is lost.<unk>  during a shallow dive differs from<unk>  during ascent from a deep dive in that<unk>  during ascent is precipitated by depressurisation on ascent from depth while<unk>  in consistently shallow water is a consequence of hypocapnia following hyperventilation.
Freediving blackout
Bristol heart scandal
Breast cancer survivors' dragon boating
Telenursing
Carney's triad
Angor animi
Predimed
Garland's triad