Quick before Shabbos
So Bill now has an official diagnosis -- an autoimmune problem called "sarchoidosis." It causes scarring on the internal organs. Happily, it appears to be treatable with steroids and is one of the autoimmune problems that frequently clears up after a year or so of treatment (although some patients require treatment for life).
Given all the things it could have been, and worse, not knowing what it was, this is good news.