While was water is still important, drinking too much water in a short period of time can lead to a condition called hyponatremia, which occurs when you have low sodium in your body. When sodium levels drop in the fluids outside the cells, water will get in there and attempt to balance the concentration of salt outside the cells. The abundance of water causes the cells to swell. Most cells can adapt to the change, but the brain cannot. When this occurs less than 48 hours after exercising, in extreme cases it could be fatal if not treated immediately.Symptoms of hyponatremia include; vomiting, loss of appetite, headache, restlessness/fatigue, abnormal mental status (hallucinations, confusion, etc.), muscle weakness and convulsions. Other factors to keep in mind when exercising in the heat include: Make sure you are sweating properly. If you stop sweating when you are exercising you are dehdydrated. If you realize your pulse rate in the morning is 10 to 15 beats higher than your normal rate, you should take the day off from exercising. Normal pulse rate is around 70-90/ minute.Get acclimated to the heat before you begin an exercise regimen. Start off with 15 minutes and slowly work your way up to 45 or an hour.Forget about the "no pain, no gain" mantra. Recognize warning signs and take the appropriate action immediately.Avoid exercising between 10 a.m. and 2 p.m., the hottest part of the day.Don't try to diet by sweating. It will only result in water loss, not true weight loss.Wear loose-fitting, light-colored clothing, and sunscreen."It's very important to use common sense when you exercise in heat," Muntz said. "If you follow a few simple rules when it comes to hydration and pay attention to what your body is telling you, you will get the results you are looking for."SOURCE The Methodist Hospital