What made my monitor’s display shift to the right by 3 inches?

This morning I was doing some training using a Pluralsight course I am taking. I needed to get up from my desk to go do something else in the room.

When I returned, I found that the display on my monitor had shifted to the right by 3 inches, making it impossible for me to see what was on the right side.

What would cause it to do that?