@SeraphisCain
What could have caused it to appear momentarily like that, just as I was shutting down?
I wonder if your heater or AC was kicking on at that exact time or maybe a power brownout or if you're using an old surge protector, maybe it time to replace it. Those things don't last forever and can wear out over time from multiple power surges. Also if you're going to replace your surge, you might as well spend a little more and get a Battery Backup which will help with surges and brownouts. I've got this one that I plug my modem/router into and my main Raspberry Pi.
And is it something I should be worried about?
If it only ever happens once, I wouldn't worry about. If it keeps happening, then it could be an issue. Maybe a short in the power cable? Bad surge protector? Dirty power?