This doesn't sound like a case for meds. What it sounds like is possibly swim bladder problem and/or neurological problems. Unfortunately, it happens. There are many causes, such as water quality, sodium chloride overdose, physical trauma, temperature jumps, and various others. It sounds to me as if the fish is too far gone to save, and is probably suffering. My personal advice would be to examine the other fish, if any, and if nobody else is showing any of those same symptoms, be humane, but put the fish down and end its suffering. I would also advise trying to eliminate causes in water quality and incompatible tank mates that may be present, but posting test results for ammonia, nitrite, nitrate, pH and size of tank, how long it has been set up, what and how much you're feeding (how often, too), if you've done water exchanges, and how many, how much water, and a list of all the other fish in the tank... and how many of each, live plants or fake, everything you can think to tell us will help. We have a lot of experienced and knowledgable people here at fishforum, all eager to help.
I will keep an eye open for your post.