My son left a 55-gal tank when he moved out. Right now all that is left in it are 2 elipse catfish. A couple of months ago, one of them acted the same as you are describing. He looked totally dead, but you could barely see him breathing very shallowly. I picked him up and moved him to a smaller tank w/no other fish because I didn't want his "friend" eating on him as he died. He didn't budge at all when I picked him up by hand. I kept trying to "right" him with a net because I didn't want him on his side. After moving him to another tank, I added some MARACYN-2 by Mardel, and kept trying to "right" him for hours. Finally after the sun came up I went to bed for about 3 hours and when I awoke, expected to find that he didn't make it.
Instead, he was swimming all over the tank!!! He/she is very large and was too big for the 10-gal tank I had put him in, so decided to move him back to his tank. (I had to go to the store once they opened to get an 8" net, and he was longer than that)
Anyway, I'm happy to say that he's doing fine. I swear by Maracyn-2 and always try to keep some at the house for such occasions (and no, this isn't a commercial, just fact). It's pretty expensive, but it has saved several fish of mine.
I never found out what was wrong with him, but the medicine did the trick, evidently.
If there are other fish in your tank, they will feed on him unless you can separate them somehow. I wish you luck and hope he makes it!
