Fibromyalgia is a similar but separate condition to ME/CFS.
Fibromyalgia (FM) is a common medical condition characterized by widespread pain and stiffness, fatigue, sleep problems and cognitive difficulties. The illness does not damage tissue and is not progressive or fatal. The severity of fibromyalgia varies greatly from patient to patient. Some people with FM continue to work, though a significant minority are disabled.
For a more detailed answer to the question, “What is Fibromyalgia ?” please read the article by Dr Charles Lapp and Dr Bruce Campbell on their “Treat CFS & FM” website.