Hi Astrid,
First, I'm so sorry you're having such a bad week - and I'm sure the stress of the holiday season does not help one bit.
It can be especially tough dealing with family or friends around holidays. One thing I have found to have worked for me is to give them a heads up before I arrive that I'm not feeling up to par and I'll do my best to stay as long as I can. This way, they are on "notice" that I may not last the evening and they won't be surprised if/when I have to make an exit.
This doesn't mean it's easy, but it's one thing to try! Hope this helps and let us know what you deide to do.