In physiology,<unk>  is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mild<unk>  can also be caused by immersion diuresis, which may increase risk of decompression sickness in divers. Most people can tolerate a 3-4% decrease in total body water without difficulty or adverse health effects. A 5-8% decrease can cause fatigue and dizziness. Loss of over ten percent of total body water can cause physical and mental deterioration, accompanied by severe thirst. Death occurs at a loss of between fifteen and twenty-five percent of the body water. Mild<unk>  is characterized by thirst and general discomfort and is usually resolved with oral<unk> .<unk>  can cause hypernatremia (high levels of sodium ions in the blood) and is distinct from hypovolemia (loss of blood volume, particularly blood plasma).
Dehydration
Altitude sickness
Water intoxication
Postural orthostatic tachycardia syndrome  Postural orthostatic tachycardia syndrome  1
Hyperosmolar syndrome
Hypovolemia
Exercise-associated hyponatremia
Stress hyperglycemia