If you don't think it's going to be that sort of illness, the two drops of Rescue Remedy under the tongue, or arnica, or getting the person to take deep breaths using the lavender oil. You can make a simple rehydration drink with a half teaspoon of baking soda and one teaspoon of salt to a quart of water. You may just want to moisten the lips with this, if drinking is going make them vomit. Quarter-cup doses every 15 minutes would be a wise recommendation. Again, if they're unconscious, certainly offer nothing to drink, although you could apply Rescue Remedy topically to their wrist, forehead or neck.
Heat stroke is the most serious, and can be fatal.
With heat stroke, you should seek medical attention. The signs of heat stroke are the person loses consciousness would be the extreme, but also headache, dizzy, disorientated, people wander around acting as if intoxicated. You wonder if they're drunk, but they could have heat stroke. Heat exhaustion and dehydration can go along with this, but dehydration is simply being without fluids to the point the mouth is dry, the body is not urinating, the eyes look sunken, and dehydration can also be very serious and might occur from lack of fluids, too much sweating, or a long bout of diarrhea. When it's really hot, I suggest drinking lemon in water rather than ice water.