Prepared to Beat the Heat? I was in Las Vegas recently, and after about an hour by the pool, I started to feel light-headed. When I went inside, everything went dark, and I collapsed. I was fine after a few minutes, but the incident scared me. Did I have a heatstroke? Based on your description of what happened, you may have experienced heat exhaustion -- not heatstroke, which is far more dangerous and is considered a medical emergency. Heat exhaustion can develop when you sweat a lot and don't replace lost fluids. As in your case, the symptoms are generally transient, but they can be scary. To prevent heat exhaustion, be sure to drink plenty of fluids -- water or a sports drink -- to replace the fluids you lose through perspiration. Eating salty foods can help you retain water, but don't take salt pills (they can irritate your stomach). Rather than lying by the pool, you might have avoided the symptoms you developed if you had taken a swim or at least dunked yourself (or dangled your feet) in the cool water. When you're planning to exercise in hot weather, avoid the heat of the day. Instead, exercise early in the morning or in the evening, make sure you get plenty of fluids, and cool yourself off afterward with a shower or a swim. Heatstroke is much more serious than the scare you had. You could say a heatstroke is the opposite of hypothermia: Your body can't regulate its internal temperature -- heating up faster than it can cool itself down. You can become confused and disoriented, have convulsions, and lapse into unconsciousness. Without appropriate treatment, kidney failure or permanent brain damage can occur. A study conducted after a 1995 heat wave in Chicago found that heatstroke claimed 600 lives. Roughly half the patients treated in intensive care units for heatstroke died within a year. The elderly and the ill are the most vulnerable, but no one is immune from the effects of intense heat. Be sensible in hot weather: Always drink plenty of filtered or purified water (before you get thirsty!), avoid alcohol, wear loose-fitting clothing, and spend as much time as possible in air-conditioned areas.