Help! Betta not eating/sluggish after fin rot treatment

[Tinsel]

OK. I'm new here, but I decided to register as I really need help. My otherwise perky little HM betta's fins had gotten progressively worse even with frequent water changes, so without consulting the internet, I went to the local aquatics shop to buy a bottle of anti-fungus medication. Pimafix was the only thing they had - and now that I look online (too late!) it seems that this is no good for bettas, even dangerous.

I put my betta in a separate container and added the medication while cleaning his normal tank. He was in it for maybe an hour, probably less, but when I came back, he looked really sluggish. So I put him back into his (by this time cleaned) tank, and he sank to the bottom and had difficulties swimming. After a while of helping him stay up via a separate container within the tank, he looked a lot better, and I released him into the bigger tank. I thought he'd recuperate quickly in his clean tank.

The problem is... that was two days ago now. He ate before the whole medication disaster, but has refused to eat yesterday nor today. Despite him swimming around a little, he is NOT his perky self. He often just hovers completely still, swims away and hovers again. He almost looks as though he's in trance.

I'm devastated.

I love this little fish. Before this whole fiasco, he'd often come out of his little hiding spots to "greet me" whenever I came into the room. Now, I feel like I may lose him because of this one silly mistake - nowhere on the bottle of Pimafix does it say it can't be used for bettas!!!

Does anyone have any experience with this? Can I do anything at all??

PLEASE HELP!

[LebronTheBetta]

Okay. Does he look bloated? Does he have a difficulty swimming? If you said yes to both, he may have SBD, also known as Swim Bladder Disease. It's like being constipated and that he can't swim properly because of it. Oh, and is the Temperature low? Maybe it's the reason of the sluggishness.

[Tinsel]

He doesn't look bloated, and the temperature is fine, too (there's a heater in the tank, and I even raised the water temperature a little by adding warm water).

Apart from his fins looking crap, he was absolutely fine prior to the Pimafix treatment, and I am pretty sure that something went wrong because of this treatment. He can swim now though one of his pectoral fins is less active than the other. But he is still sluggish, and won't eat...