The main difference between heat exhaustion and sunstroke is body temperature. If the person's temperature is 40°C then medical help is needed and quickly!
Apart from the obvious measures of getting the person into the shade and cooling them down with cool water or fans; these natural remedies bring quick relief from the symptoms (headaches, nausea, excessive sweating, dizziness, fainting).
Peppermint Essential Oil
Peppermint Essential Oil improves circulation and blood flow to the skin, hence it not only feels cooling it actually does reduce body temperature. It also soothes the nerves and helps alleviate nausea.
Simply add 2-3 drops to a cool wet cloth and place behind the neck as well as on the forehead. A few drops mixed with a carrier oil is safe to massage into the wrists, temples and soles of the feet of small children (Aloe Vera is a good choice because it also has soothing and cooling properties).
You can also make a peppermint spray by mixing 20 drops of Peppermint essential oil in a 125ml water spray bottle. If possible, a soak in a cool peppermint oil bath is a quick and effective way to reduce the temperature and calm the person.