I have since noted that the display is actually on, but extremely dark or dim so that I can barely make out what is on the screen.
New twist. I kept the laptop power on. Came back to it about 45 minutes later, and the screen is completely visible, as though nothing was wrong. I re-booted. Still ok. I have no idea if I did anything to cause it to dim or reappear. But this disappearance and reappearance has occurred 2x. Is there something about to die on this unit?