Long time ago, while running cat5 in a large open ceiling, I stepped off of a large metal beam onto what I thought was the concrete ceiling of an outdoor awning, but was in fact droptile. Fell right through, of course, and landed more-or-less on my back. The floor was that hard institutional carpet.
I don't remember anything about the fall itself. After hitting the floor I immediately got to my feet, realized the breath had been knocked out of me, tried to call my partner's name, then sat back down. I think the pain came shortly after that.
Reminds me of a short story by Alastair Reynolds, "Glacial". In it, scientists are studying these worm-like alien creatures that seem to interact with one another via chemical markers left on the tunnel walls. It is theorized that they're acting as a sort of distributed intelligence, although it's really slow due to the extremely low metabolism.