Ok, I noticed that the Retroarch setup screen was the blue menu (older version?) vs the green checkered menu so I was really worried about some sort of weird corruption so I restored the image from a backup and all is now well again.
Friendly reminder of the importance of good backups! :-)
Incidentally, does anyone know know what the difference is between the blue menu and the green checkered menu in Retroarch? Is the blue version an older version?