Today I came home from work to find my red-tailed catfish at the bottom of the tank upside down, kind of arched. He is still breathing and swam around a little bit, but it seems that as soon as he starts swimming normally his body uncontrollably flips upside down. His skin was black and is now gray with black spots and his tail does not have the red color anymore. Does anyone know what this means or anything I can do? The catfish is about 4 years old.