Good evening, I am very sorry to hear about Freddy's situation. If he was initially bottom sitting, this suggests that there may have been an issue with his water (ie nitrate toxicity) or he may have been suffering with an internal issue (ie bacterial septicaemia). That said, to see the erratic swimming and arching as well as buoyancy issues (which could be swim bladder), I am quite concerned that he may be reaching a terminal state in his condition. Therefore, while you could consider checking water parameters, broad spectrum antibiotics and treating for constipation, I would suggest that since he is in discomfort and his signs so advanced that euthanasia be considered. In case you have not euthanized a fish before, I do want to include a link regarding the use of clove oil to do so (LINK) without letting him suffer. Please take care, Dr. B.