In my years of keeping fish, if they swim like that it's only a matter of time before they go belly up. The info you found on the web regarding swim bladder is probably pretty accurate. If it's an internal problem or bacteria related Maracyn-two should fix it, if given within the right time.
If you're in an area where fish meds cannot be found do yourself a favor and order the largest you can afford from someplace on line. I'd suggest Maracyn-Two and Maracyn to start with. You may also want to get MarOxy and Maracide for those one off problems you may run into.
Been my experience, esp. when I started back up a year ago that you'll need fish meds and it's better to get them early on. Once you have good tank conditions then you're more likely not to need them too often.
Sometimes you'll get sick fish from LFS
and that's a bummer. Learn their policy on returns or replacements if the fish goes belly up. Also be sure to watch the fish at the store for a fair amount of time. Also ask when the new fish were introduced, that way you can determine if you can actually get healthy fish from the tank.
Some of this you may have already known, but since I don't know your background I thought I'd try to cover a wide range. If you do know it, then great, just filter out what you do know.