A few days ago, my neighbor offered to coordinate her friend coming to look at my computer, which was hibernating, going black, and seemingly short before I could even enter my log in credentials That's when I used my smartphone, since it was unaffected, to do a little research; and when I discovered that the model of computer I am running is prone to such glitches, maybe not prone, but it's not unheard of.
Well I did the old unplug/re-plug Microsoft cold reboot trick. That not working, I just let it alone. I did, however, try it once more, the morning before it was to be examined, it seemed to work just fine as before.
I seem to remember a notice on the notices screen it was going through an update/maintenance cycle.