Ouch. Show quality, how old is it?
Is it defecating? If it isn't it could be intestinal problems.Don't feed it DRY pellets. Soak the food before feeding it to goldfish to avoid air bubbles in the food. And don't overfeed it, especially since fancy goldfish have a tendency to eat every single thing fed to them. Most of the swim bladder problems in goldfish is caused by digestive problems.
Also change the water and clean the filters. It could be bacterial or viral, in which case it'd be easier for them to recover if their environment is cleaner. As always be careful when moving them around when cleaning tanks. A sudden change in water temp can kill fish, but I'm sure you know that already. I think it's also recommended to move the fish to a shallower tank to lessen discomfort.
Also the pea thing is simply about taking care of possible impaction of food in the digestive tract. And yeah, I think it's also worth a try.
But I'd be very careful concerning treatment, if this is an old fish. It would really suck if it died. Why not ask a vet first?
In my fishkeeping days, I've had several die of it.
One was a 3-4 year old black moor that was already showing the bronzing of age... it was my favorite of the bunch too.
We didn't have goldfish specialists here back then.