Please help, my axie seems like he's having spinal issues :(

Https://www.youtube.com/watch?v=AG9C8VCDCv8

Pardon the murky water in the video, I did a tank rescape last night and kicked up a lot of sand.

My other two lotls are fine. Sagan has always been a bit shy so I don't know how long this has been happening but he seems to be having trouble moving. I noticed a few weeks ago that the right side of his belly has the normal curve to it while the left side was flatter, and it seems like when he tries to swim around he's curved towards the fatter side of his belly. He also keeps his back legs higher than his head and seems to have trouble doing more than wiggle them.

I don't keep any rocks smaller than large, flat, river stones so he can't be impacted. This is making me so sad and with all my knowledge about these guys I have no idea what this could be or how to help. I've had Sagan for 3 years.

Is this bacterial? Paralysis? Muscle loss?

Have you ruled out constipation as a cause?

Not yet... I'll keep an eye out for poos but it honestly doesn't seem like his back end is floating, just twisted