I do not have fibro but I see the same types of fatigue with the different pain issues I do have. The fatigue and fog can be over-whelming at times if I do not move enough.
I have found it is huge benefit to make sure I get up and move around, be it taking a walk in the summer or in the winter walking around inside my house for a set period of time, long enough to get my heart rate up so it lets my body know that I am getting exercise.