Well, everything continued working fine for the rest of the session, I also restarted once or twice to be sure everything was fine. After that I went into one of the VR worlds for awhile... then powered down and went to bed.
Today, I turn the machine on, it starts loading Windows, gets as far as the Starting Windows splash screen, where the colored dots coalesce into the Windows logo... and it hangs (if it helps, it's at the point when there's three little dots set diagonally). And all disk activity stops. What could this mean?
(Turns machine back off, restarts it...)
It recommended Startup Repair, so I let it do that. Seems to be taking awhile.
Okay, after maybe 15 minutes of that, it came back with the recommendation that if I'd added some new device to the computer, please uninstall it and start it again. Should I have let it go back to a previous storage point? Last time I did that, several programs I'd just installed all magically vanished... and I wasn't wanting to go through THAT again.
BTW, this hang-at-startup thing is exactly what it did at this time yesterday.
(Lets machine shut off, starts it again...)
Hmmm, this time it started okay... Will simply leave it running for a little while without doing anything to see if it gets goofy.