It will be okay, AniManic. I hate sharp mood swings, too. I have them all the time, it is really hectic in my head.
I say that when I'm reallying cycling I will dial it back, but still try to function. So for your dinner party I say to pick a menu that is really easy, a dish you make all the time that you could do in your sleep, so to speak. That will take a lot of stress off, I think. Don't worry so much about decorating or being fancy. Just be casual with it.
I hope your dinner party goes well and you start feeling better! I understand how frustrating it is to lose focus and not work the way you think you should.