UNless you fed him something he shouldn't have (some types of lettuce are poisonous to guinea pigs) then chances are, it could have been stress (easy child leaving, and being a one person guinea pig) or maybe just getting old. Guinea pigs don't live very long.
My vote is either stress, or something he ate/drank. They are incredibly fussy - chemical sprays can contaminate their dishes and can be enough. Or sometimes they just get sick suddenly.
Check the teeth - if a guinea pig's teeth are not meeting properly, they can overgrow and not grind against each other, so the guinea pig eventually starves because they can't eat properly. It's not always easy to spot when this is happening, but not quite a year old - that could be a possible cause too, because it can take that long for the misshapen teeth to overgrow enough to be a problem. And if thta was a problem, easy child should have spotted it and taken the guinea pig to the vet to get his teeth rasped back down. Long-term, a guinea pig with teeth not wearing properly either needs a jaw realighnment or frequent trips to the vet lifelong, to keep cutting the teeth back.
So have a look at the teeth. The ones to check out are thelongest ones at the front (top and bottom). The molars - less likely, but check them out as well.
I hope for your sake it's the teeth. Then you can blame easy child. Or the poor thing's bad genes.
Marg
