It's a very weird scenario. I never saw a fish with that kind of symptom due to the lack of oxygen. I wouldn't discard some other causes. Something related to the swim bladder or neurological causes will be a good guess in my opinion.
Hails from Brazil
D.
What possible Neurological cause? I guess someone with the know how could have told the exact cause after a postmortem. This part of the death of my fish troubles me the most ... Cant pin point the exact cause. All possibilities are logically arrived at not scientifically.