CHRONIC FATIGUE SYNDROME
Chronic fatigue syndrome is a debilitating and complex disorder. It causes severe fatigue, weakness, muscle pain, an inability to concentrate and insomnia.

FIBROMYALGIA
Fibromyalgia is a chronic disorder of the muscles characterized by fatigue , sleep disturbances, and tenderness.

According to Ramona W. of Edmonton, Alberta, Canada, who suffers from both: "Fibromyalgia is chronic fatigue syndrome with pain." There are similarities, and there are differences. Most patients of both disorders suffer from sleep disturbances, headaches, depressing and a numbness or tingling of the skin.

The Fibromyalgia Research Blog talks about the symptoms as compiled from a survey:

The most common problems were morning stiffness, fatigue, nonrestorative sleep, pain, concentration, and memory. Aggravating factors included: emotional distress, weather changes, insomnia, and strenuous activity.

Familydoctor.org describes the symptoms if chronic fatigue syndrome this way:

People with CFS experience fatigue that lasts a long time. Symptoms may include headaches, sore throat, tender or painful areas in your neck or armpits, unexplained muscle soreness, pain that moves from joint to joint without swelling or redness, loss of memory or concentration, trouble sleeping and extreme tiredness after exercising that lasts more than 24 hours. These and other symptoms often won't go away or keep coming back for 6 months or more.

When diagnosing chronic fatigue syndrome or fibromyalgia, doctors must first rule out several other disorders. These include virus infections, mental illnesses, obesity and sleep disturbances which, in this case, are causing the symptoms instead of resulting from them.