For other people, CFS develops after a bout of infectious mononucleosis ("mono"), which temporarily saps the energy of many teenagers and young adults. Often, people say that their illnesses started during a period of high stress. In others, CFS develops more gradually, with no clear illness or other event starting it.

A hangover that does not go away even after adequate sleep. The extreme weakness of chronic fatigue does not go away. It continues to drain the person for months and years.

Typical symptoms include muscle and joint aches, fatigue, and weakness. Other possible symptoms include abdominal pain, alcohol intolerance, bloating, chest pain, chronic cough, diarrhea, dizziness, dry eyes or mouth, earaches, irregular heartbeat, jaw pain, morning stiffness, nausea, night sweats, psychological problems such as panic attacks, shortness of breath, skin sensations, tingling sensations, and weight loss. CFS symptoms either hang on or come and go frequently for more than six months. For most people, CFS symptoms plateau early in the course of illness and thereafter wax and wane.

Women are three to four times more likely to develop CFS than men, but researchers aren't sure why this is so. When the disease was identified in the early 1980s, it was called the "yuppie flu," because most of those diagnosed were well-educated, well-off women in their 30s and 40s. Since then, doctors and researchers have found it in both men and women, of all races, ethnic groups, and ages, although it is still more prevalent in women. There is evidence that the disease (under other names) has been around at least since the 1800s. In the 1860s, physician George Beard named the syndrome "neurasthenia," because he thought it was a nervous disorder that caused weakness and fatigue. CFS also is known as myalgic encephalomyelitis, postviral fatigue syndrome, and chronic fatigue and immune dysfunction syndrome.

And because the symptoms are vague or are similar to other diseases, CFS is difficult to diagnose. A complete history and physical exam are needed to rule out conditions that mimic CFS. In certain cases, blood tests may be ordered to rule out diseases like multiple sclerosis and systemic lupus erythematosus that take years to show symptoms. Even after a tentative diagnosis of CFS, new symptoms might show that the problem is something other than CFS.

Scientists are not sure what causes CFS, although many theories have been put forth, including anemia, hypoglycemia, allergies, yeast infections, and the Epstein-Barr virus. At this time, no one knows the cause, although CFS seems to involve interactions between the immune and central nervous systems. It does not appear to be an infectious disease, passed from one person to another.

No treatment is available for CFS, but certain medications can ease some of the symptoms. Non-steroidal anti-inflammatory drugs (NSAIDs) can ease body aches and fever. Antihistamines can alleviate a runny nose and other allergy-like symptoms. Low doses of antidepressants may help with sleep problems. A rehab specialist can help plan activities for the times when a person with CFS has the energy to do them.

These statements are all rumors that have circulated about CFS, but none has been proved.