There are a number of possibilities. It almost looks like the spine is broken or something. Is the body unable to bend in one direction anymore? It could also be an internal infection of sorts, particularly one affecting the brain that could lend itself to vertigo or impact motor control. It doesn't look like a swimbladder issue to me because the overall buoyancy is relatively normal, but I suppose the pain of added pressure could make it not want to bend to one side. It is rare for a fish to recover from constant spinning. They have trouble getting to food.