I think this would be a good deep dive discussion for the AACC podcast.
I’ve certainly experienced this for hours at a time, on basically no sleep during ultra endurance races. Usually you get the other end of the spectrum too though, where you experience massive lows where you barely have enough energy to even stand up or pedal at 100 watts and a you want to do is lay down and cry/sleep.
I think at some level it’s a deep flight or fight response, and your body protects itself and it’s organs by making you feel awful so you’ll stop and rest. There’s always energy there though, and sometimes a surprising amount of it.
I think the other aspect may be that what you feel you’re doing might be massively different from the numbers of what you’re actually doing during those peaks. Going through a low and then having power “return” may not really be happening. The powers probably still really low relative to a fresh version of yourself, but you feel okay mentally so it feels like your producing more power than your expectations.