This is a very old remedy of mine, hardly a home remedy.
Research studies have been done on decades ago what is needed to prevent heat exhaustion and/or heat stroke. It turns that people susceptible to this were found to be deficient in magnesium, vitamin C, and of course water with some appropriate electrolyte salts to prevent dehydration.
I once had a friend who was extremely heat exhausted, and as a trial I gave her magnesium and vitamin C. Over the course of a week in 100 Degree Fahrenheit heat, she could stand the heat much better than me since I didn't take the supplements! The usual dosage for magnesium is 250 mg of magnesium chloride or similarly magnesium citrate, but never magnesium oxide or magnesium carbonate.
For vitamin C, it is necessary to take about 1000 mg per day minimum. It is important that in hot weather you will loose a lot of valuable salts from your body. So if you do not have an electrolyte salts or sports drink (one bottle/day will do), you have to add about 100 mg of potassium citrate or potassium chloride to your drinking water, besides just the usual 1/4 teaspoon per liter of water of sea salt.
A couple of years back, a health conscious Sports television broadcaster died while playing a simple game of tennis. The diagnosis was a somewhat vague "heat exhaustion". However, there was more to it then that. People also loose valuable minerals besides salts from the sweat, such as chromium, selenium and others. When this happens, a mineral deficiency is possible and you can just collapse from such condition without any warning. It is therefore necessary to supplements yourself with mineral supplements in general also.
For most older people death is quite common during a high heat most of the issue has to do with dehydration. For some reason or another old people simply do not know when they need water. When people get older, their sense of thirst becomes dull. It is this reason why people as they get older appear dehydrated or die of dehydration whenever there is hot weather. I have observed that people's sense of thirst starts getting dull as early as 40 years of age. Therefore it is necessary to monitor the body's thirst by some other external means instead of just relying on our own instinct.
Most standard way of drinking plenty of water that we all heard of is the volume of water, or how many liters of water you drink per day, or how many glasses of water you drink per day. Usually there is a consensus of 8 glass. This I disagree. How much you drink pretty much depends on the temperature of weather. It would be ridiculous to drink 8 glass of water while the temperature is below freezing. It is hardly enough water if you are running 100 mile marathon and just drink 8 glasses of water either. What happens if you are 8 foot tall and another one is 4 foot tall? Do you think BOTH will drink the standard 8 glasses of water?
Therefore, I have suggested many people here to use a newer standard of determining how much water is enough, depending on your own body's physiology. It is not perfect, since we don't have rocket science equipment to gauge it, but it is the best that I can come up at the moment!
One way you can track WHEN YOUR BODY NEEDS water is to observe the color of your urine. A light yellow color is the standard. Any color darker or deeper then this means the body is really out of water and you don't even know it. However this is not an accurate gauge for sudden hot weather scenarios. It just track whether you GENERALLY drink enough water, or the day. It is a rough measure.
You also need a second measure also: the frequency of urination. In case the urination is not frequent, you need to take note of the frequency of your urination under MODERATE temperature. Assuming that over the course of the day, you urinate say 4 times. So in a very hot weather, the frequency of urination should remain constant. If not, you are simply not drinking enough water. You can make an approximate time between urination also, such as every 12/4 (12 hour day/4 urination = 3 hour), every 3 hours you should urinate, plus or minus say 1 hour. If you don't urinate within this range, THEN DRINK WATER! It can save you your life from dehydration, especially if your don't know you are thirsty!
Most senior citizens have this problem, but I make it a point for 40 and over. However, in practice, people of all ages should use this method. The older the more fatal it is. Young people don't die, from dehydration, but they do die from mineral/salts exhaustion!
In summary take plenty mineral supplements of magnesium, and vitamin C. Often times, take mineral supplements also. Don't forget to drink sports water. And finally be sure to gauge the color of your urine and the length of time between urination.
With the suggested method of monitoring my own thirst by observation rather relying on my own instincts, I have found that my body needs more than twice the amount of water in a hot weather. It is my bad habit that if I don't monitor them, I will often get dehydrated by drinking less than half of what my body needs. This could be potentially dangerous as this might introduce heat stroke or heat exhaustion.
There are other special considerations:
For people with diabetic conditions, heat exhaustion can be more serious. Therefore, they need to make their schedule of how much water by establishing THEIR OWN STANDARD color, and frequency urination UNDER moderate temperatures on the basis of the amount of sugar in their urine. I used a Brix refractometer, to measure the ideal sugar urine not to exceed say 3-4 brix. Then I will drink enough water slowly over say 3 hours and check for the exact color, and do the exact frequency of urination over the course of the day to get the urinary sugar in a safe range. As a rule a diabetic will drink about twice more water than other people at moderate temperature, so that the blood sugar does not get over at toxic level.