Heat Stroke

Heatstroke is a condition caused by your body overheating, usually as a result of prolonged exposure to or physical exertion in high temperatures. This most serious form of heat injury, heatstroke, can occur if your body temperature rises to 104 F (40 C) or higher. The condition is most common in the summer months.
Heatstroke requires emergency treatment. Untreated heatstroke can quickly damage your brain, heart, kidneys and muscles. The damage worsens the longer treatment is delayed, increasing your risk of serious complications or death.
Symptoms:

• High body temperature
•  Altered mental state or behavior
•  Alteration in sweating
•  Nausea and vomiting
•  Flushed skin
•  Rapid breathing
•  Racing heart rate
•  Headache 

Prevention:

• Wear loosefitting, lightweight clothing.
• Protect against sunburn.
• Drink plenty of fluids.
• Take extra precautions with certain medications.
• Never leave anyone in a parked car  
• Take it easy during the hottest parts of the day.
• Get acclimated.
• Be cautious if you're at increased risk.