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Even more dangerous is cold water shock, which likely causes more fatalities than hypothermia. Cold water shock occurs when a person experiences sudden, unexpected immersion into water 15° or below. For three to five minutes after sudden immersion in cold water, a person will gasp for breath and may also experience muscle spasms and a rise in heart rate and blood pressure. The instant muscle spasms and gasp reflex can cause the victim to involuntarily ingest water and drown. A rise in heart rate and blood pressure can result in a heart attack or stroke.