HELP! Fish is dying RIGHT NOW!

I've got a scavenger fish (bottom feeder) that I thought had been sick with fungi for the past week and a half. I added aquarium salt and fungi clear and been adamant about water changes. It wasn't getting better but it wasn't getting any worse so I thought he was just slow at healing.
I left for a few hours with my friends and he was eating in his corner like normal. When I came back he couldn't swim away from the filter. When I turned off the filter he kept swimming on his side. Now he continuously goes belly up and only swims if another fish pokes him or I do. I don't know what to do! someone help!

[OceanOz]

Is your bottom feeder a Pleco? I've had a lot of problems keeping them, they seem to die for anything. They're very sensitive to temp, pH, and the amount they eat. How often do you change the water? Changing it is important, but doing it too often can wreak havoc on the pH balance. Also, I would recommend ALWAYS having a bottle of  Melafix on hand as antibiotics are always a good thing to have and won't hurt your fish even if they don't need it. What kind of food are you feeding him? Are you sure he's eating enough? Too much salt, even aquarium salt, can also be hard on a fish. Also, using an anti-fungal when it isn't needed can be hurtful... without more info, I can't really give any specific advice.