Heat exhaustion is the next step beyond simple dehydration. Because of a large loss of body fluid, the circulatory system can collapse, causing a sudden drop in blood pressure, which can lead to unconsciousness. Because heat exhaustion is the next step past dehydration, it gives a lot of warning signs before its onset. Increasing fatigue, severe cramps, weakness, inability to think properly or strange behavior, drenching sweats, dilated pupils, and nausea are all warning signs of heat exhaustion. A person with more severe heat exhaustion can have cold, pale, clammy skin, be agitated or disoriented, and can complain of profound thirst.
Heat exhaustion is a serious medical condition.
The first step is to get the victim in a cooler environment. Out of the sun at the bare minimum. Elevate the feet about twelve inches and have them lie down on a flat surface. Elevating the feet helps keep blood flowing to the brain. Apply cool clothes, wet compresses to the skin of the victim.