Oh man OP, I can relate. A similar thing happened to my cat and what she had been eating. The trouble is that pancreatitis and similar complications are much harder to detect in felines so it cost us $1300 to repair our kitty.
She's ok now and the vet still couldn't put a precise thing on the cause guessing it was either being hit on the belly hard or falling wrong on it (less likely since she wasn't bruised but she's an out/indoor cat so we don't alway know what she's up to)... or a terrible diet that her body cannot support and honestly, everytime we'd eat fast food we'd give her something with beef since she loves it! Especially Arby's roast beef.
It was just a scary time. Had I not been home to notice she wasn't eating or going outside, she wouldn't be alive today. Even the vet said her intestines weren't pink and they had to go in and work them into working again, she was that close to dying
Lesson learned, animals can't eat a lot of things we do.
But I hope doggy feels better soon and I feel your pain, it's a scary feeling knowing a family member is in trouble. I hope the recovery is fast and I am happy that dog has a loving family that can offer support in the time of pain.