That would be the sound that woke me up this morning.
In my what-the-hell daze, I went looking for something that the kitties had knocked over or something.
Water was dripping from the gaping wound in the ceiling.
When I installed the air conditioner in the room above, it was a much smaller unit than the one that had been in the window previously. And the condensation drain didn't quite extend past the sill, so all of the condensate was running down the inside of the wall and into the ceiling below.
Interestingly, what is up in the ceiling looks to be wallboard, which means that it was already repaired once.
I did a temporary cover on the sill upstairs. Eventually I'm going to have to figure out how to fix it permanently.
Right now I just wanna lay down and nap.