In many FMS patients, fatigue is as big a life-destroyer as pain. There are many possible causes of fatigue. Some people feel it's due to abnormal nervous system responses. Others blame low levels of growth hormone. Still others think it's caused by inhibition of the chemical reactions that burn sugar to create energy. Whatever the cause, fatigue can be debilitating. Among fibro patients who go on disability, most cite fatigue as the primary reason.

One treatable factor that worsens fatigue is poor sleep. Even the healthiest people will experience fatigue without a good night's rest. But it can also be brought on by stress, anxiety, and a busy schedule. In people with FMS, the situation is made worse by unrelenting pain and the stress of having a chronic condition. Many patients find, however, that if their sleep is improved with medications, fatigue is reduced.

Muscular fatigue is also a major problem in FMS sufferers. Many people with fibro note that they are physically incapable of activities that used to be commonplace for them, such as walking through a grocery store, picking up their child, or doing routine job activities like typing. It's easy to imagine how devastating this could be for someone living alone, or how many problems it could cause for a FMS patient's family. In some people, muscular fatigue may get so bad that they are confined to a wheelchair.