Hottub?

You basically cook your organs when you're in there. You can get heat exhaustion that will progress to heat stroke. Those are are symptoms of heat stroke. Your friend needs to stay cool (but not too cool), refuel himself with electrolytes (by drinking sports drinks), and keep himself hydrated. This stuff you learn when you're training to be a lifeguard and you need to dig people out of a hot tub when they've been in there for too long...happened to me more than enough times.(hope i help)