Fibromyalgia is a chronic, long-term illness. It causes all-over muscle pain, joint pain and fatigue. The pain may come and go. is a chronic (long-term) disorder defined by pain and tenderness throughout your body, as well as fatigue. It causes all-over muscle pain, joint pain and fatigue. The pain may come and go. It is a long-term condition that causes pain and tenderness all over your body.