There is a very seasonally germane (for those of us in the Northern Hemisphere)
article in the New York Times by their very good science/health writer Gina Kolata about new research on heat stroke. One issue is that nobody really knew about long term affects and when it is safe to return to exercising - kind of like where we were with concussion some years ago. One paragraph to pique your interest: "But autopsy studies and some MRI scans of people who had heatstroke indicate the hypothalamus is not damaged. Injured brain regions include the cerebellum and the cerebral cortex, which is why people pass out, Dr. Sawka said. He worries about lasting damage to the liver and kidneys. One study of distance runners who had heatstrokes and repeated liver biopsies indicated their livers were still recovering four months later. And a study by the Army's Research Institute for Environmental Medicine found that 30 years after soldiers had heatstroke they were at increased risk of death from liver failure and other organ damage."