It's kind of sad that they think that. But, how are they supposed to know how you feel. I usually now answer "fair on the fibro-scale", which means pretty darn bad on the well-person's scale of how are you.
Fatigue & accompanying "Fibro Fog' that comes from pushing past crushing, relentless, mind-numbing pain. It's way past my level of endurance, at times. On top of that - put on the *Happy Girl Face* for everyone else's benefit. It's exhausting.