I've seen gouramis spin at my LFS (so much for quality...), and I doubt many (I'd even say any) fish survive this. Most fish that lose control of their swimming wind up dying. Parasites, though, are not something I'd expect to be the cause. Not that I know anything about it, I'm just surprised. Well I suppose it could be if they're the internal kind. But I'd think it'd be something with the swim bladder. Do parasites affect it?