Hi, Pat. So sorry to hear about your chi.
We haven't had experience with Addisons, but for a while the vets thought one of our dogs might have had it--although it turned out to be IBD, the onset and symptoms were similar to what would have occurred with Addisons. With Evan the symptoms came on very rapidly, too--one day he was fine, then rapidly went downhill the next. So I don't think it's an unusual course of events for either disease.
How is Arnie doing now? Did they get him diagnosed and on the mend?