He refused to eat for two days.
He was up for snuggles and attention, but if I introduced a bit of food into our space he would immediately stop purring and turn his back on us. I'm no cat psychologist, but it seemed that he was just being a jerk at that point.
I went out and got some cat "junk food" - his favourite crunchy treats, a can of Fancy Feast, some weird chicken "rope" thingies... For about 7 seconds it seemed like he might stay on the couch as I shook the treat bag, but he was unable to resist. Perhaps just getting anything into his stomach made him feel just better enough to try eating meals again. To start taking his heart medication again.
I've never had an aging indoor cat before. My parents' cats were all forced outdoors so when they got sick or injured they simply... disappeared. I don't know how to deal with declining felines. I don't know how to decide whether it's time to begin his traumatic end, or if he's just a day away from bouncing back. What if we're wrong?
BUT HEY, LET'S DO THIS.