Yoyo loach dying? Its not Playing!!?

Sounds to me like he may be the victim of bullying. Do you notice the other fish chasing him or pieces missing from his fins? Even fish that are smaller than him can bully him. The only thing I know to do is move him, which you have already done. I would just keep him in a separate tank with the light off for a while until his condition improves, if it does. He could just be really really stressed. He may die anyway. I'm sorry if this wasn't very helpful, I don't know why else one fish would be acting sad and the rest acting fine. :(