I think I may have had a bad bag of Hill's C/D dry food. Storm just threw up after eating it, and Ambercat was refusing to eat it. Just opened up another bag and he wolfed it right down.
Ambercat is pretty much himself again. He has to have a blood test in a month to be sure nothing is going on, but 99% sure it was just an infection of some sort. https://www.youtube.com/watch?v=1VLGrSRr8Ds