How to re-enable scrolling in InDesign on Creative Cloud

I use keystroke commands a lot to navigate around.  Every now and then I press something by accident in InDesign and have no clue as to how to get out of it.

This time, advancing through a long doc a page at a time by keystrokes suddenly stopped working as the result of a faulty keystroke command on my part.  (Ctrl-PgDown)

I can click on the scroll bar at the right, and the mouse will scroll, too, but both are clunky and slow.

I wondered if I'd depressed the NumLock key by accident, but whether it's locked or unlocked, the pages won't advance page by page with a keystroke command.

I also looked in Edit\Preferences, but there are so many sub-menus to look at that I gave up trying to find something.

So I ran a couple tests:

1. I opened a different InDesign doc to see if the lack of scrolling is specific to the document I was working on, or to all of them.  All docs are affected. 
2. As I had a .pdf open, I used the number keys to scroll page by page, and that is working fine.

I am using InDesign in Creative Cloud with the latest update.

I hope someone can decipher this!  Thank you.