So that's what that was?

I was in my classroom planning, sitting at the computer in my rolling chair. I felt a strange rolling, waving, rocking, very mild and my first thoughts were:

I'm imagining this
My ear problems are acting up
Someone has upset the universe
Finally, the HVAC system right behind is working too hard.

So I stood up, turned around, and it quit.

Didn't think more about it until this evening when I heard it could be felt far away.

The building didn't shake nor did we evacuate. No one even mentioned it. I think I must have felt the tremors under the building. My ears have been extra sensitive for a few years.

Glad everyone is okay.