If he seems healthy - i doubt he is dying.. i really wouldn't worry about it, just make sure he eats, check his scales, make sure his glowing and he'll be fine! (oh - and, i don't know if his on his own or not, but if he isn't.. make sure the other fish aren't picking on him.. In fact, if he isn't alone, what other fish is he with???)
PS: I happen to love Black Moors, they're great fish!
PSS: Here's a little website (below) that'll help you incase something occurs on your fish, it has a list of diseases, etc, that are common for goldfish, and any other fish at that. Good luck.
http://www.kokosgoldfish.com/disease.html