Fibromyalgia strikes an estimated 4 million to 6 million Americans. It's especially common in older women. Dr. Don Goldenberg, a medical advisor at the Arthritis Foundation, says 3 percent of women have fibromyalgia at age 40; 7 percent by age 70.

Goldenberg, also chief of rheumatology at Newton-Wellesley (Mass.) Hospital says about 80% of those with fibromyalgia suffer from extreme fatigue and sleep disturbance, while irritable bowel syndrome plagues as many as 70 percent of sufferers. Other common problems, in addition to depression, include anxiety, headaches and cognitive problems.

For Mary Anne Saathoff, president of the Fibromyalgia Alliance of America and herself a sufferer, it was leg pains and sleep disorders that began as a child and worsened with adulthood.

"I felt more dead than alive," says Saathoff who was diagnosed in 1986 with fibrositis — fibromyalgia's precursor name. "It certainly takes a great toll."

No Proven Cause, No Known Cure for Fibromyalgia
The medical community has only recently started to get a handle on fibromyalgia. In the 1980s a few specialists began developing treatments for the non-fatal condition, and in 1990, the American College of Rheumatology gave the syndrome its name. Within the last decade, researchers have learned more.

"We no longer think this is a disease primarily of muscle," Goldenberg says, "but one of the central nervous system."

While researchers have not proven what causes fibromyalgia, there are a number of theories, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

The leading theory is that fibromyalgia is caused by a disregulation or imbalance of neurotransmitters in the brain like serotonin, which helps to ease physical pain.