[Gpdd] Health: Piggie in Pain

[vachins at comcast.net]

Hi, I'm a lurker on the list with 2 gpigs of my own, Keats and Francesca.  I'm asking a question about my sister's gpig, Guinea.  This morning, after eating some of his pellets and parsley, Guinea started running around his cage and jumping like crazy.  Than, he went and hid in his house and would not come out.  My sister picked him up and she said the only sign she noted was that his heart appeared to be racing.  Since this behavior was so odd, my sister took him to the vet who said this was likely a sign of pain.  He did not have any appreciable amount of gas, and he appeared to be over his distress.  Tonight, he is calm and happily eating, drinking, and playing with his water as usual.  My question is whether anyone out there knows what the cause of his behavior/distress might have been.  His bodily functions seem to be fine, he has no blood in his urine, and he has no other signs of health issues.  Any thoughts about what might be happening here?  Guinea is 4 years old and very sweet and friendly.
Jeanine