The document grids are no longer visible. I've switched them on/off, rebooted the computer, all to no avail.
There is a Document Grid. It can be turned on and off in this location: View > Grids & Guides > Show Document Grid.
It would also not show if you had turned on the Preview screen mode. This hides all edges, guides, grids and shows a print preview. To turn on Normal screen mode, choose View > Screen Mode > Normal.
Thanks Steve--discovered I was in Preview mode without realizing it. I never use Preview, I prefer Shift > W so I'm not sure how I got into Preview. In any case, all is well.