Drowning is a respiratory impairment caused when the bronchial tract is immersed in a liquid, usually water.  The body's autonomic response results in the opening of the mouth in an attempt to breathe, followed by a reflex action of the glottis which shuts off any possibility of fluid reaching the lungs.  As a result, the victim suffocates.  The victim can often be resuccitated at this stage if they are taken out of the water, but if water enters the lungs, the prognosis is much worse.

A near drowning event is a medical emergency and requires immediate medical attention.  Complications can arise for up to 72 hours after a near drowning event, such as swelling of the bronchial tubes.

Drowning at Wikipedia

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