Also of note, it's great to "take a break" in the afternoon, but that doesn't necessarily mean you have to take it WHERE YOU'RE STAYING.
While it's nice to go back to your room or timeshare, take a dip and/or a nap, and while you're not allowed to jump in the pool at a Disney resort if you're not staying there, you could, if you wanted, opt to take a bus/boat/monorail/stroll to a Disney resort, have lunch there, shop in their stores, a drink at their bars, play in their arcades, whatever at that point in time floats your boat.
The main houses or buildings of each resort are always air conditioned with plenty of couches to put your feet up if you want; while I'd suggest not napping, I don't know if anyone would wake you up as long as you didn't look homeless. It'll afford you a chance to get out of the sun and the hustle of the parks, but also afford you the chance to check out some of the Disney resorts. Maybe that'll be the incentive you need to stay in one next time.
And when you're rested, head back to the parks.
You could also visit Downtown Disney if you wanted, though there will be no direct bus from a park to DTD. You could take a bus to Saratoga Springs or Old Key West, then boat from there (if you get dropped off at one of the extreme edges of Saratoga Sprigs, you could even walk).
In fact, if you're REALLY "feeling the heat" going to a Disney resort may even be preferable to getting in the car, if you're suddenly feeling too wiped out to drive. Though if you properly anticipate when you'll be exhausted and start heading out 45 minutes or so before that point, you'll probably be most refreshed by going back to your own place. Just wanted to point out, there's options.