I didn't see that sweating guy from last night at the exercise place. It could be that he lost so much body fluids, became dehydrated, and is now a pile of sand down by the beach. Of course I wouldn't wish that on anyone. But I do believe it's theoretically possible. After all, sand has to come from someplace.
I myself was working up a sweat tonight, nothing quite like his but still substantial. I wiped my sopping brow a couple times and looked at a handful of moisture that formerly was inside me. What moisture's doing inside your forehead, I'm not sure. I can move my head back and forth and I don't hear any sloshing. So I'm assuming there must be sweat veins parallel to the blood vessels.
They told us in science class that sweating is the body's way of cooling itself. Like an air conditioner. And we've all seen air conditioners dripping everywhere. In that case, having had a great workout, I can expect to be frozen solid within the hour. A big body popsicle. The harder you workout the colder you get.
It's a great feeling to have a vigorous workout.