A 39-year-old woman reports diffuse musculoskeletal pain for…

A 39-yeаr-оld wоmаn repоrts diffuse musculoskeletаl pain for the past year. She complains of non-restorative sleep, chronic fatigue, headaches, and intermittent abdominal cramping. Physical examination reveals diffuse soft tissue tenderness without synovitis. CBC, ESR, CRP, ANA, RF, TSH, and vitamin D levels are normal. Which statement best explains the suspected diagnosis?