Heat exhaustion is one of the heat-related syndromes, which range in severity from mild heat cramps to heat exhaustion to potentially life-threatening heatstroke.
Signs and symptoms of heat exhaustion often begin suddenly, sometimes after excessive exercise, heavy perspiration, and inadequate fluid or salt intake. Signs and symptoms resemble those of shock and may include:
If you suspect heat exhaustion:
Call 911 or emergency medical help if the person's condition deteriorates, especially if fainting, confusion or seizures occur, or if fever of 104 F (40 C) or greater occurs with other symptoms.
Infomation from: http://www.mayoclinic.org/first-aid/first-aid-heat-exhaustion/basics/art-20056651