Thank you for the reading recommendations Cassius.
For me the katastematic "pleasure at rest" is a mental sense of satisfaction and gratitude, a quiet feeling of joy...when everything is fullfilled. So it is like a cat sitting in the warm sun and purring, and enjoying the sense of aliveness. It isn't a permanent state. And many modern people might prefer to "keep busy" in life and so miss out on experiencing the quiet kind of pleasure. Modern life is noisy, and active entertainment is everywhere. I can imagine that back before modern technology, "pleasure at rest" was even more enjoyable when shared with good friends.
Perhaps my viewpoint comes from past dabbling in Zen meditation (and modified by a Theravadin approach of sitting for the feeling of bodily enjoyment). I admit that the "pleasure at rest" sense of satisfaction doesn't happen for me very often. But I wonder if Epicurus might have taught this in the Garden. And if it was lost, though it's not something that easily translates into words.