Poor thing! I can only think of bugs sometimes insidiously crawling from inside. Reminds me of one of my Beucarnea Recurvata when it started going downhill...as well as my upright Sedum, doing similar, though did not find anything even after I checked on the roots.
Any changes on your temps/weather? I notice my desert rose is thinking it is Fall, starting to dry out its leaves when we had a sudden 10 degree variance. So maybe your pachy is just starting to wind down for Fall..though a bit early I think..but then again weather is crazy these days.
