Prius completely lost engine power *after* mountain pass

I have a 2008 Prius with 203k miles and a refurbished hybrid battery installed at 190k miles 1.5 years ago. The vehicle works very well.

Yesterday we drove over Sonora Pass in California (Route 108). Over a long stretch, you go from sea level to 9600 feet. The last stretch is quite steep. I did not take it particularly slowly and you can really hear the internal combustion engine run noisily. I've done this many times in California over various mountain passes.

It was also an unusually hot day yesterday in the mountains. It was in the 80s at 7,000 feet and still in the 70s at the summit. I did not turn off the air conditioning. Perhaps I should have, but I've done done it in the Prius.

Coming down the pass, we found ourselves at a relatively flat area around 7,500, and I started noticing the engine sputtering a little bit as we went over gentle uphills (there is still a little bit of uphill--up and down--even as you come down the mountain).

Then, relatively suddenly and in a flat section, the car just lost forward propulsion. I was able to get to teh side of the road at about 1 mph. No check engine or other warning light came on.

I turned off the vehicle and popped the hood, thinking perhaps the engine was overheating. There, of course, was no smoke, and there was no burning smell.

A couple of minutes later, I started the vehicle up, turned off the a/c and drove gently to the next town (Bridgeport, CA). The car drove just fine. At a gas station I topped off the oil, adding 8/10 of a quart to get to teh top of the dots in the dipstick. (It had been about 2500 miles since the last oil change; I thought the car consumed more like 1 quart every 5,000 miles, but that's what I found.)

We then drove rather gently for another 30 miles in 80-degree heat outside with no a/c before I turned the a/c on again. The car drove just fine.

So here's my question: Could the car have overheated a bit over the pass and lost power for that reason (even though no engine light came on)? Or is it more likely that something else is wrong with the car, such that I should be worried that even taking the drive more gently coming home and without a/c that I won't make it? I'm traveling with ai 2-year-old....

Thank you in advance for any advice! I should add that I did have the coolant control valve replaced several years ago. I also replaced the spark plugs at 145k miles. My engine air filter is pretty clean. I'm also using regular, conventional 5w30 oil, not "high-mileage" oil.