I just went through this with my Jester bun.
How I knew something was wrong: he would huddle up in the corner of his pen, he hadn’t eaten his veggies, pellets or hay. He had zero interest in his most favorite treats. We took him to the vet and they did x-rays- they didn’t see any blockage but could see parts of his intestines that were darker colored. The vet’s best guess was that it was gas. She listened with the stethoscope and could hear sounds and could feel cecum (which is a good sign, she said).
They prescribed metoclopramide. They also gave him subcutaneous fluids to keep him hydrated.
At home, we took a big plastic syringe and filled it with mushed up pellets in water and fed it to him. That seemed to stimulate his appetite and he started eating on his own within a short time.
His tummy was making the LOUDEST gurgling noises that night.
We continued the metoclopramide for 5 days.
We’ve cut out veggies for right now (as we are thinking they were the culprit). He’s now only getting timothy hay/mountain grass, pellets, water and papaya tablets (the enzymes are supposed to aid digestion). We will slowly introduce veggies to him again, once he seems to be alllll straightened out. 
I thought I was doing well by following the HRS’ recommended veggies, but something didn’t agree with Jester!
He is doing great now!!!!!!
Now I feel like we can better handle this if it happens again.