This is weirder.

It could have been a truck going by, though I didn't hear any. It could have been the wind, though the pattern was more a gentle shaking than a swaying. It could have been a small earthquake, though none were reported online. Or it could have been that we have extremely large squirrels living in our walls.

In any case, the other morning, the bed started shaking while I was still in it. The sensitive drawer pulls on my nightstand rattled, confirming the motion.

Or maybe the house is just settling. Very, very quickly.