INDD Page distortion -- What have I done?

INDD 20.2 Windows 11/64

I shut this project down and went to eat supper. When I got back, this is how I found one of my pages. I suppose I caught and dragged something witha stylus or mouse and then saved it, having had no idea what I did.
My questions are: How do I undo it (if I can)? and what did I do, so I won't do it again.

Thanks to those who know more than me,
Joe