In other words, x: 0.0" is in the upper left corner, as expected, but y: 0.0" is in the lower left corner. I don't know how this happened!
How do I set the ruler so that both the 0.0" coordinate for both x and y is in the upper left hand corner (as is standard in most programs)?
You can change the page origin by dragging from the location where the rulers meet.
You can also use a VBA macro to set the page origin to match your preferences.
Both of those are mentioned in this thread: Page reference issue in corelDraw 2019...0,0 not where it should be!
Thank you, Eskimo!
I still don't know exactly what happened, but if I can fix it, it's okay.