After a while, I correlated the problem to very high humidity: usually happened during heavy fog or rain. So, it's probably an ignition problem, right? Replace spark plugs. Nope. Distributor cap/rotor. Nope. High performance plug wires. Nope.
Drove me nuts for about two years. Then one day I'm in my garage looking for something and I move my timing light out of the way. Hmmm, didn't think about that...
After two years, problem turned out to be timing slightly out of spec. Fixed in five minutes!
I had a similar issue that turned out to be a slightly loose battery connection. While the battery clamp was making contact with the battery terminal, I didn't tighten it enough and it made poor contact.
Is it correlated to temperature at all? If it is, I wouldn't be shocked if something, like a relay, is building up heat and increasing resistance to the point of operating incorrectly. A short nap might give that component enough time to cool off.
Randomly during longer trips, the car will just die for no discernible reason. It's the Car of Theseus at this point with how much I've replaced, but the issue persists, and the nature of these intermittent problems makes debugging a nightmare. More puzzling still that the car starts up fine after a short nap.