We had that too. In fact, twice. Caused by an imperfect bathtub install
that left a crak between the tub top and the tile. It was all fixed.
However, I will not easily forget the experience of hearing tiny sounds
like grit falling, seeing the ceiling slowly come loose and just before
getting the drop cloth down to get the ceiling, seeing a piece of plaster
of about ~3x5 ft come down in the living room while still standing in the
kitchen.

I was only out of the shower a minute or so when the ceiling fell in
where I had just been standing. Sheesh!

Ron