I know it wasn't a Studio update, because as stated, I redownloaded an executable demo compiled several days back, and it's suffering from the same problem. That basically rules out any issue with the file itself, as far as I can tell; something else on my computer updated, and now a file that previously worked fine, and was not even present on the hard drive the time of the restart, is misbehaving. I'm also reluctant to believe it's anything as "simple" as a damaged fan or bugged graphics driver, since far more demanding games and other programs are functioning at their usual capacity. Aside from this one particular issue with the one game that I'm developing, I'd never have even assumed anything changed.
And that's what honestly makes it so perplexing. All evidence points to the issue originating on my computer, and yet there's nothing discernably wrong with my computer, save for its interaction with this one very specific game. I don't even know where to start looking for the hangup, and I'm not quite desperate (nor knowledgeable) enough to start messing with the machine in ways as drastic as switching out to older operating systems. Or for that matter to blow money on expert analysis and repair, when for all I know whatever issue I'm experiencing will be patched within a week by whoever caused it.
I appreciate your thoughts, and I'll keep them in mind if the issue takes too long to resolve, but I guess what I really need is just someone who's already experienced and resolved...whatever this is.
Edit: I will try defraggler, though. Who knows; if it works, it works, if it doesn't...hopefully it won't destroy my PC.
Edit 2: After messing around a bit, I'm beginning to suspect that it was an Intel driver update that caused this. Unfortunately, the option to rollback is completely greyed out, so I guess I'm going to need to uninstall it and figure out which version I had yesterday.