Hi, I’m not sure if this is a general health question or a behavior question. However, it has me really concerned!

I’ve had rabbits for awhile and have a vet that works with them. While I’m not a super level rabbit manager< I'm experienced in their case. I have a 4 year old Mini Rex neutered boy. He’s been healthy and had no issues at all. Until this morning…. When I woke up today, he was his fine and typical self. I showed him a snowball from outside and he was interested in it. My mom fed him (I am an adult but just had a double organ transplant so I’ve been told to avoid his pen, not to clean it, etc, because of bacteria from poop.) and he was his normal self, *My mom feeds him all the time since after my surgery because of this and I rely on her to get it done. Well, he went for a tear around his pen. Throwing everything around and pushing the liners/bedding out of the way. Then, he would throw himself down. Wait a few seconds and then throw himself down again. He did this over and over. I picked him up to check out his back legs and they’re mobile. His belly felt really loose too. So, I put him down on the floor (carpet) to see if he’d be more comfortable there. He’s not. He’s getting up, digging at the carpet and throwing himself down. To me, it looks like colic in horses. I’ve had bunnies that had digestive problems but they weren’t eating and lost their energy. So, I took them to the vet and hand fed them until they were better. But this I don’t know… I’m trying to see if he’s still breathing heavily (like after his tear up and getting up/down a lot) but he’s behind a table leg now! Oh, if it matters, when he lays down, he always goes into porkchop position. I rang the vet but today is his in clinic surgery day so I probably won’t hear back from him until late afternoon. Does this sound like anything to you? Digestive? Musculoskeletel? Other illness? Thanks in advance… I’m so scared!