Aches and pains with no obvious cause? Constantly tired despite getting plenty of rest? If you answer yes to either question, you may have fibromyalgia or chronic fatigue syndrome. Or possibly both.

Fibromyalgia and chronic fatigue syndrome are two conditions characterized by their difficulties: difficult to diagnose, treat, deal with and, for some patients, even to prove they exist.

Fibromyalgia causes chronic widespread pain and multiple tender areas known as trigger points. Patients also often experience insomnia, fatigue, headaches, memory difficulties, depression and other symptoms.

Chronic fatigue syndrome (CFS) is marked by profound, long-lasting fatigue. Patients rest but cannot shake the overwhelming feelings of tiredness. There also other symptoms, such as impaired memory, sore throat, tender lymph nodes and muscle or joint pain. These patients usually wake up feeling tired and fatigued in the morning.

Both syndromes are more common in women than in men. And in each condition, the cause is unknown.

Differences and similarities

So what are the differences between fibromyalgia and chronic fatigue syndrome? It depends on whom you ask.

Some experts think they might be two names for the same condition. Between 50 and 70 percent of people diagnosed with one condition could just as easily be diagnosed with the other, according to the Arthritis Foundation.

In fact, a physician's familiarity with each disorder may influence the eventual diagnosis. For example, a doctor with a long history of treating fibromyalgia is more likely to diagnose this condition than CFS.