This is extremely sad and disturbing. I'd be losing sleep being totally depressed. I really, really sympathize.
My instinct tells me these chickens are trying and failing to cope with the heat, and I bet it's humid heat, too, right? What makes me think this is in your initial post you mentioned you found your chickens in a hollowed out depression. This is what all warm blooded animals do when trying to cope with very hot weather. But it does little good unless the hollowed out depression is cool so that excess body heat can be transferred to the cooler soil. I've watched little desert ground squirrels do this when it's 117F. They race around in the hot sun on 150F gravel and suddenly head for a shady spot under a tree and pancake flat for a minute or two, and they're off and running again.
Whether an animal is wearing a fur coat or a down jacket, the reality is that they are stuck wearing what they were issued and can't remove it when they get too hot. So these animals seem to instinctively understand the second law of thermodynamics - heat flows to cold, and if they can find some cold, they will be able to discharge the excess heat into the cooler material. Fans may help move the air around, but they don't do much to help discharge the body heat effectively.
When it gets very hot, I water down the sand in the entire run so my chickens can burrow down into it and discharge the heat buildup in their bodies. This is the quickest, most efficient method since most of the blood vessels in chickens' bodies are on the breast and wing pits. The beak, feet, and comb also release excess body heat, so I provide frequent dishes of ice cubes for them to play with which cools the beak and feet as they shove the ice around and drink the melt water. I haven't even bothered with electrolytes in the drinking water because these cooling down strategies are so effective.
If in spite of all your efforts a chicken become lethargic and overcome by the heat, cooling down the individual immediately is crucial. Take the collapsed bird indoors and place cold compresses under the wing pits and along the breast bone. Do not dunk the bird in a tub of ice cold water, though, as this sudden temperature change will kill them. Once the bird is revived, provide electrolyte water with extra sugar for them to drink. The chicken should respond immediately unless there is something else going on.