So far, so good on zapping the PRAM. (knocks wood)

I reset the NVRAM on my Mac (aka "zapped the PRAM") and so far it seems to have resolved the problem.

This is a simple procedure of restarting the Mac, and holding down the Command, Option, P and R keys once you hear the startup sound. You hold them until the Mac reboots again, then release them. This clears hardware settings that are stored in non-volatile RAM (NVRAM), resetting them to the system defaults.