Ayden, I don't think we've met yet, but I've been following your posts about Hewbie for a while now. I'm rooting for him!
My tilefish was also floating upside down when he got severely constipated and refused to eat for a few days. It was a very scary sight! I built little shelves at several different levels all over his quarantine tank so he could anchor himself better and float underneath them instead of being pushed around by the flow.
He eventually got better after about a week, the constipation cleared out and he started swimming upright again. Hoping for the best for Hewbie too!
In the meantime, this might help:
https://www.reef2reef.com/threads/causes-of-abdominal-swelling-in-fishes.1098720/