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 intake. Signs and symptoms resemble those of shock and may include:
Feeling faint or dizzy
Rapid, weak heartbeat
Low blood pressure
Cool, moist, pale skin
If you suspect heat exhaustion:
Source Mayo Clinic