This happened to my dwarf gourami. It started out like a cut on his lip. Then it got worse, and eventually his lip kind of fell off. He was not active, and didn't eat much, but was very bloated. He devolped a welt looking thing on his side, which was exposed flesh I think now. Anyway, he died a horrible death, and during that is when I found this site. Nobody ever really knew what it was. Possibly a cut that went infected. Also, I had new tank syndrome for a few weeks before so that probably weaknd him too. I tried different meds, but nothing helped. None of the other fish were infected. It all happened over a couple of weeks.
Sorry to ramble, but I hope this helps....