Googling reveals that a lot of people get this problem, though few seem to know what the source is or how to fix it, and it took me a long time to find the solution. Though I finally did (at least, it works for me):
- press the Windows key
- type "Calibrate display color" and press enter
- When the Display Color Calibration window pops up, press "next", then simply close it.
- Done. The screen should now be bright again.
I still don't know why the problem exists, or why doing the above fixes it, but it seems to fix it every time.

Dave is a graphics professional and longtime PC power-user. He spends more on his gaming rig than a reasonable person should. He founded the indie game studio Volnaiskra, and is the creative force behind Spryke.