If you think you are suffering from a heat related illness seek medical attention. I am only offering this as a preventative, as in HYDRATE!
After getting way too hot a couple years ago and spending over a week in a terrible state I keep this recipe on hand at all the times.
2 Quarts water
1 teaspoon baking soda
1 teaspoon salt
1/2 teaspoon salt substitute (potassium chloride)
7 Tablespoons sugar
1 cup fruit juice
This recipe is also great for animals which have gotten too hot or dehydrated from scours or excessive heat. Replace the fruit juice with Karo Syrup.
Once you've gotten into a heat emergency situation you will always be more susceptible. Keeping hydrated is the easy prevention.