Heat cramps are caused by a lack of salt due to excessive sweating. The sodium and chlorine in salt are electrolytes, and your muscles need them to function properly. Heat cramps feel like regular cramps -- the muscles in your legs, arms or stomach constrict, causing discomfort. When you feel the cramps setting in, stop walking and get into some shade and off your feet. Drink some water and, if you have it, add some salt to your canteen. If you've been saving that sports beverage, drink it -- it has a good amount of salt. After some rest and hydration, your cramps should go away.

Heat exhaustion is caused by further loss of water and salt. Some signs that you may be suffering from heat exhaustion are:

Headaches
Irritability
Excessive perspiration
Weakness
Pale skin tone
Vomiting or nausea
Cold and clammy skin
Fainting

Treat heat exhaustion much like cramps. Get in the shade, sit down, elevate your feet and drink water. If you have enough water, douse a towel or bandanna and apply it to your skin. Loosen your clothing and fan yourself.

Pete Turner/Getty Images
This mirage in the Namibian desert looks like a pool of water. But it's not. It's sand, nothing but sand.

Heat stroke is caused by a complete failure of the body's heat-regulating system. This means your body temperature rises rapidly and you're unable to sweat and cool down. The symptoms are:

Severe headaches
Dizziness
Nausea and vomiting
Muscle twitches or spasms
Confusion and aggression
Very high body temperature and hot, red skin
Increased heart rate
Hallucinations
Unconsciousness

Treat the same as heat exhaustion. Find shade, lie down, elevate feet, loosen clothing and drink water. You should also pour water on your skin and have someone in your group fan you vigorously. You could die from heat stroke, so it's no time to save your water. If you have some cool compresses in your first-aid kit, apply them to your armpits and groin area -- two areas that will help lower your overall body temperature.

What could it be? It's a mirage
A mirage is an optical illusion caused by the reflection of light that can make an object appear distorted, closer to you, or above or below where it actually exists. Mirages form when light rays are bent as the path of the ray crosses layers of air that have different densities. The technical term for this is refraction. You can see refraction at work by placing a pencil in a clear glass of water and looking at it from the side. The pencil will appear bent at the water line.

Air at different temperatures has different refractive indexes, which is why you're likely to see a mirage in the heat of the desert -- the ground temperature is much higher than the air temperature. The cliché image of a desert mirage is an oasis appearing closer than it is. The thirsty hiker runs toward the haven and shovels sand into his mouth, thinking it's water. This is a cinematic exaggeration of a how a real mirage looks. In truth, an oasis can appear closer than it is, but you wouldn't mistake sand for water. You can learn more in How Mirages Work.

On the next page, we'll read about desert dangers that crawl, bite and sting.