I have gone to
Fibromyalgia - Wikipedia, the free encyclopedia and I am trying to summarise and paraphrase it into simpler language so hopefully you can understand.
It affects 3-6% of the population.
It is also called muscular rheumatism.
The main symptoms are all-over pain and tenderness to light touch.
Other symptoms MAY include: heightened sensitivity of the skin (also called allodynia), tingling of the skin (often needle-like), achiness in the muscle tissues, prolonged muscle spasms, weakness in the limbs, and nerve pain.
The above means that sleep is often disrupted or of a poor quality.
It is not fatal, and does not harm your body over time.
It's just a permanent pain. There are no outward symptoms, you have to believe your mother that she is in pain.
The disease isn't accepted by all doctors, since there are no outward symptoms. It may be a mental illness, with the patient's brain creating the pain.
I hope that this is a good start to you understanding the condition. If you have other questions, please ask and I will do my best to find an answer for you.