@dlowan,
She only ever did that once before....when she was desperately sick.
Perhaps she is now so old that the invisible (to my human nose) smells of that earlier episode led her to think in her sleep that she was in the litter box?
Hmmm...I guess there's no point in getting a new mattress until after her death, if this sort of thing is going to happen.
The whole place now reeks of the white vinegar I have used to try to clean up after her.
She also totalled my goose down pillow.
Or perhaps she knows that shortly I shall deliver her to the vet for boarding for TWO WEEKS!!!
She has been very quiet this last week...but her fur looks good, and she has been eating well. And is very happy and responsive when I spend time with her.