Sometimes they'll just sit on one place for a bit, possibly to smell/listen to their surroundings, or perhaps sometimes to just take a quick rest. Mine will sometimes have her ears down for a minute when she first wakes up, almost as if it takes her a bit to fully wake up and perk up her ears.
It could be that your chin was just experiencing some digestive discomfort from eating something she shouldn't have. If the symptoms resolved, then it's likely whatever it was safely passed through her system.
Oats can cause gas in chins, and while they used to be recommended, it seems that now people are advised to stay away from oats in lieu of other treats that are less gassy (like the ones on Amethyst's list). If you do choose to give oats, it's best to offer them in extreme moderation (like maybe one oat a week, if that).
Trust me, I know how annoying it is that there's so much misinformation about what chins can eat! When I first rescued my girl, I wrote up this list of safe and unsafe foods and posted it in the kitchen, so my roommate and I would have a quick and easy reference.....only to find out a couple of days later that it was totally outdated information and that none of the things on the "safe" list were actually safe.
(Fortunately Margaret, the chin, hadn't touched any of the fresh fruit we'd tried to give her, so no harm done....she clearly knew more than we did, haha.)
It still wouldn't be a bad idea to take her to a vet, just to get a general wellness exam and to get her listed as a patient with a good vet. That can make it easier to get seen quickly if you ever have a real emergency. It's also just a good idea to have any new pet looked over by a professional, if only to just get some peace of mind that she's in good health. I usually try to get my critters in to see a vet within the first month or so of getting them for those reasons.