Excellent point. I cycled in Phoenix with a guy who nearly died of this on a golf course one summer. He said it was a stupid thing to be out when it was so hot, but he was very well hydrated. The last thing he remembers before waking up from his coma days later was wiping his brow and thinking, that's odd, my sweat is slick. No salt in the sweat leaves a clean feeling and that's a sign you're about to die, apparently.