I'm afraid I can't remember anything that specific. I did fall through the floor once just a few rooms before so when this loop of it began I thought it was a joke, and the momentum kept increasing so it went faster and faster for a while, but then it reached a speed and stayed there and then I knew it was a bug, I left it on for a few minutes just to make sure.
Perhaps the high momentum was what kept pushing me through the floor?
Speaking about this though, I noticed every now and then when going through a door I'd go maybe half a meter down and instantly stand back at full length, it seems to me that it's this moment where the falling through floors thing happens.
Perhaps always have the room under spawned in so you fall into another room instead of into the void?