I'll take a look and see if it's just battles. Might be.
Nowhere near RAM limits; this is now a lower-than-midrange gamer box, but it has 16 gigs and I'm almost never close to actual max (and wasn't when this occured).
You might be onto something, TJJ, but... it was paused when Windows activated Sleep Mode. Surely it was mainly just doing a whole lotta sleep() and not having to do a lot of new math each frame? I know that pretty much all of the code I was running that was my stuff halts when we're paused; I might want to check OS status as well, though.
Probably what I'm going to do is turn Sleep off and just dim my screen instead. I've never used Sleep Mode before and I really don't want things like this crashing while I'm doing other stuff; I was about to fight a crazy-huge test-battle to do more playtesting on Rebal and lost access to that scenario because my save was 20 minutes before I'd gotten into it, lol.