I once had a goldfish that was about 12 years old develop what I believe was a brain tumor, as his head was semi-translucent enough to make out some sort of internal growth. He exhibited "seizure-like" episodes very similar to your video, where he would lose ability to regulate buoyancy for short periods of time, several times in a row, and then return to near normal. He lived like this for several months, although after one bout of seizures he stopped eating normally. He would still eat, but he almost had to push around in the sand and stumble across pellets; he also stopped swimming in open water stayed near either the sand or decor. I think he developed some sort of vision loss, and was navigating by lateral line or something like that. One night, he suffered what was clearly some neurological electrical storm and basically seizured to death.
I'm sorry not to deliver better news, but I'd have to agree that your fish's issues look similar to my experience, and it appears neurological. Could your bass maybe have hit his head? Some sort of internal trauma? Best wishes that he may recover!
