2. Heat Stroke
Your body needs to be at just the right temperature to function properly. Internal bodily temperature can be adjusted when you overheat slightly, such as by sweating. However if the rise in temperature is too sudden or goes on for too long without relief and hydration in the form of water, sweating may not be enough as a cooling mechanism. This is when the body can literally short circuit to gain temporary relief, just as when bad wiring causes power to go out or your laptop overheats and switches off.
Heat-related illness can cause a rash or cramps, or severe conditions such as heat stroke, which can even be more fatal. The elderly are more susceptible to heat stroke as their bodies cannot adjust quickly, or because there are other underlying conditions at play as well. In the general population, those most at risk of fainting from heat stroke are those over 65, babies, pregnant women, people with high blood pressure or lung disease, and those on medication for mental illness.