That sounds very unpleasant @Magnolia82 - I hope that the painkillers help. I really don't think it's from low carbing, more likely either an allergic reaction to something, or something viral. I'd definitely go and see either your local pharmacist or your GP (if you can get an appointment).
@catwithflowers that's always a difficult dilemma. I know you've said that there are other people going, but why aren't your needs important?
If the hosts are good friends, I see no reason why you can't tell them what you're doing, and therefore what you can/can't eat. Have they not asked you in advance if there's anything you don't or can't eat? Any good host would surely do that! If you can't make your needs known because talking about 'dieting' can seem trivial (even though it really isn't), you could also reframe it as a health-related requirement - pre-diabetic, blood sugar issues, etc.
However, as you posted your question yesterday, all of this is probably a bit late!
In circumstances where you can't avoid it, just go with the flow. If you can, avoid the really carby stuff, or just eat a small portion - but if you can't, e.g. if it's all plated up, or it's all carby (like a pasta dish or a rice dish), then just enjoy it. And then be super strict for the next few days.
But never forget - your needs are just as important as anyone else's!