The heat wave that we just endured was with us long enough to make some people very sick and most of us very miserable. Fortunately the temperature and most importantly the humidity are back to more reasonable levels. The flip side to that advantage is that any adaptations that our body has made to adjust to the heat will be lost within a week. So be forewarned, a single heat wave doesn't give your body a chance to acclimatize so you'll need to be every bit as careful when the next one rolls around, which it will. So let's focus on some key rules.
First rule: when the heat and humidity rise, avoid the heat as much as possible. Give your body a break of at least an hour or 2 every hot muggy day. The time out could mean doing your grocery shopping in an air conditioned mall or going to a movie. Also, take more time to do everything not only so you won't build up more body heat but tempers flare during heat waves and so taking longer to do things and slowing down may help to avoid the increase in stress and violence that we see as the temperature goes up.
Second rule: stay well hydrated. Luckily there is liquid in many foods (for example: tomatoes, cucumbers, grapes, cherries). Vary your liquids. If you replace lost fluid with water you will not replace the natural salts and minerals that you lose in very small amounts (but which can easily add up if you're sweating a lot). If you use electrolyte drinks cut them or juice half and half with water to reduce the sugar load. The amount you drink can't be predicted. Don't wait for thirst to guide you as you will already be behind. You should be going to the bathroom throughout the day and your urine should be pale yellow, almost transparent.
Lastly, be alert to the signs that the heat is getting the better of you or someone you're with. Feeling unwell, sick to your stomach, light headed, headachey or any change in behaviour (being befuddled or confused) are all serious signs. Get out of the direct sunlight and into shade. Even better get into a cooler area. Take off all unnecessary clothing, discretely! Fan them and spray them with cold water or apply cold compresses or ice packs to the neck, armpits, groin and call for help. If they're completely with it you can give them something cool to drink but if there is any question better not to risk them vomiting and choking.
There's a famous, at least among doctors, quote: it doesn't take long to fry an egg or cook a neuron (a brain cell). You have to take the heat seriously. Remember to take the same precautions with your pets, children and look in on neighbors if they are alone.