Thanks, Sanjay. Appreciate it. I guess choking is a possibility I hadn't considered; not sure what that would look like, but I don't think so, as they didn't eat too much (just picked) and this was more than 12 hours after it was removed. There were FDBW in the tank when he started looking bad so if he had a problem with anything it was them, but he never seemed to struggle to break them up, and hadn't totally gorged himself (as usual) before he went down.
You guys are great to commiserate, by the way. If I didn't have tank space issues already I'd start angling on how to get y'all to send me fish! (Though I'm not sure that would be in their best interests! )