WATCH: Hikers are dying in triple digit heat. Here's how to survive.

Five hikers have died this month out on the trails in Arizona in triple digit weather. One of the most lethal and frustrating things about heat illness is that sufferers are often completely unaware of their own symptoms.

When you're over heated, your cognitive ability and your capacity to make a rational decision are compromised. Athletes will say they're fine and keep training and hikers will keep trudging on.

So know the signs: a high body temperature, red, hot, and dry skin, lack of sweating, and a rapid pulse. The person may stumble or appear clumsier than usual. Headache, nausea, and dizziness are also common symptoms.

If you think a person is having a problem, even if they don’t- err on the side of caution. Insist they get into the shade and cool down. Give them water and rub them with ice or a cold cloth or spray them with water. If they don’t cool down quickly, seek medical advice.

To prevent getting to that point do NOT take the chance and exert yourself in excessive heat. Even the most experienced, fit, and well-prepared hikers can be overcome by the heat.

Stay safe during a heat wave. There are a lot of other things to do: Drink ice water, make slushies, marathon Netflix, and stay by the A/C.