Hello!
He looked like that yesterday. The only place where he could've fallen would be in his tank, I always, and really always!- had my eyes on him when he was out. I would've noticed when he fell. He had a period after his brumation where he was really active and ran, and jumped around everywhere from the branch to the back wall and the other way around.. maybe he slipped and fell on his back while he did that?

it really came so suddenly...
It's really noticeable that he turns black when he tries to move...it really hurts him I think. But the hard, open mouth breathing concerns me, wouldn't it have been noticed on the ultrasounds of something was pushing on his lungs or any bones where broken? I can give you a list of what the vet did:
2 Ultrasounds, bones and organs seemed fine
Blood was taken, values were all fine, just inflammation values reeaally high
He got multiple shots, I think pain killer and anti inflammation stuff
He looked into his mouth, no signs of respitory
Prescribed vitamin B12 and liquid calcium to give him for two weeks, but that didn't really help yet.
Last time I was at the vet, he already told me we are just trying to better it at this point, and that he doesn't know what really is wrong with him. I want them to draw blood again today to see if his inflammation levels went down, but I don't know what else to do. I'm trying to get a fecal sample but since my boy doesn't really eat much, he also doesn't poop much.
The vet appointment is in about 7 hours, I'll update what the vet says then.
Thank you so much for your help tho, I'm really desperate at the moment.