Right. I know you want to prevent the situation. But - for whatever reason, I'm putting out the scenario that you DO find yourself in that situation. Who knows; maybe you met a hiker short on water and gave him your extra bottle, then your camelbak sprung a leak. Whatever.
Just trying to get thoughts on the two alternatives;
Walk on during the heat because you're afraid of trying to go 8 hours without water, or lie still for 8 hours, and wait for it to cool off...