Keep the water in pristine condition. Aquarium salt may help, at least to reduce the risk of infection. There are products that may help with trauma. Best way to get help is to do your own research. Many google searches will turn up great threads from some of these forums that are otherwise hard to find. Do you have a picture? I don't want to get your hopes up but I'd like to think optimistically. Just keep a close watch for abnormal behavior/bacteria/fungus/infections. If he eats in the morning and is at least on the move(even if a bit uncomfortable,) I'd say there's a great chance of recovery.