What happened?

Dad suffered a traumatic brain injury after collapsing on the driveway from heat exhaustion on Friday, August 24th after about an hour and a half of mowing the yard before lunch. The injury was the result of the fall itself. There was no indication of a heart issue or an aneurysm. He hit the back right side of the head, but in a "contrecoup" reaction, the brain rebounded to the front left side of the head, and that is the location of the primary injury.