Fibro is so confusing to deal with, and it seems to be never very stable. You could have a horrible day, then things could get better. Or, you could have a long flare. All kinds of time frames, unfortunately, and so hard to predict.
It's best to try not to stress about
it, hard as it is. I started dealing with one issue at a time, and that helped to not overwhelm me. What bothers you the most right now? Zero in on that, and start taking steps--even tiny baby steps--to find what works for you (you could always ask here, too).
Yes, I've found I've had to scale down many things in my life, but doing that has also helped me feel better. You could always attend your company Christmas party for just an hour or so, or however long you feel comfortable.
Fibro can often change our social lives, too. I've found myself not going to as many things as I used to, but if that's the case with you, too, what can you do that would still be possible, and even fun? Hobbies? Smaller and shorter get-togethers with friends? Maybe more of a spur-of-the-moment "let's get together" gatherings?
I try not to schedule much of anything as far as social outings in the cold weather or I know I would pay for weeks! Instead, I look ahead to the nicer weather for outings and gatherings. I guess I sort of hibernate more often in the cold weather. 
I think each of us has to find what works for them, as far as how much you can do, how many places you can go, what works for your pain, etc.. Take it all in small steps so you don't get overwhelmed. And remember your friends are here to help you!
Having a positive outlook helps, too. Look for the little surprises in life. Stop and smell the roses, as the saying goes. Life can be difficult, but many possibilities can be built on those difficulties. Many of us here use our faith to stand on when the going gets rough. Stay strong and know you can still have a great life, even with changes you have to undergo.
Wish you the best! 