Hi and welcome to the Fibro Family!
I did some digging and found a site that might help you. It's the government site for the ADA (Americans with Disabilities Act). I would think your employer would have to accommodate you under these provisions but you would need to read what the ADA considers 'disabled' to see if you can make your employer comply.
It sounds like the majority of people who have been diagnosed with Fibro and have continued with their doctor or have been treated for fibro would qualify. Here's the site with the information. I hope it helps...
Chutz
www.eeoc.gov/facts/ada18.html