Heat exhaustion occurs when you’ve been exposed to extremely high temperatures and often is accompanied by dehydration. Specifically, a person experiences heat exhaustion when the body reaches a temperature of less than or equal to 104 degrees Fahrenheit. There are two types of heat exhaustion. The first is water depletion, which results in excessive thirst. The second is salt depletion, which may result in nausea and muscle cramps, among other symptoms.