Help! What’s going on with my discus fish? :(

Hey everyone, I need some advice. My Discus was swimming very erratically yesterday—almost like he was having a seizure (if fish even have those?). He was darting around and moving in a really strange way.

Today, I moved him to a hospital tank to monitor him more closely, but now he’s lost all his color, and I’m really concerned. Has anyone experienced this before? Any ideas on what could be wrong or what I should do to help him?

Any suggestions would be greatly appreciated! Thanks in advance.