You don't have to do anything for a flare to start! That's happened to me more times than what I want to remember. Just try to keep the pain under control. I use over the counter meds to help me with that.
There are some good stretching exercises that really do work that are on Fibro 101. These are done sitting down. They were designed for long flights to help prevent blood clots but they work great for fibro, too. So, you can do this at your desk at work and it might just help you some. You do need to be moving somewhat to help with the pain.
I hope this flare leaves as fast as it came. Feel better!
Sherrine