What condition refers to abnormally low body temperature?

Hypothermia refers to a condition where the body temperature falls below the normal level, typically defined as below 95°F (35°C). This occurs when the body's heat loss exceeds its heat production, leading to potentially severe physiological effects. During diving activities, the risk of hypothermia increases due to exposure to cold water, which draws heat away from the body much more rapidly than air. Recognizing hypothermia is crucial as it can impair cognitive functions, motor skills, and ultimately the ability to make safe decisions while diving.

The other options, while important in their own contexts, do not relate to body temperature regulation. Nystagmus involves involuntary eye movements and is not related to temperature. Hypercapnia refers to an excess of carbon dioxide in the bloodstream, often due to inadequate ventilation, and does not pertain to body temperature. Arterial gas embolism occurs when gas bubbles enter the bloodstream, typically due to rapid ascent, leading to various symptoms that do not include low body temperature.