What Happens

In some cases, chronic fatigue syndrome (CFS) develops after an illness such as mononucleosis (mono) or flu, or after a period of unusual stress. But it may also develop without warning, even if you have not been sick.

The fatigue may come upon you gradually or quite suddenly. Because fatigue can be vague and can be caused by many things, you might not pay attention to the problem for several weeks or months. It is hard to say what is normal with CFS because the diagnosis often is not clear for some time.

In general:

• Symptoms are worse at the beginning.
• Later, you may feel better for a time and then feel worse again. Or your symptoms may disappear entirely. Many people improve in a year or two and do not have a relapse. Some people continue to have severe fatigue and other symptoms for many years.

Some people find the fatigue, pain, and thinking problems caused by CFS greatly hamper their lives, but other people are not nearly as affected.

• Most people are still able to perform some of their usual activities at home and work, but they often are unusually tired after they do them. People often have to cut down on social and recreational activities to save their energy for work and family.
• Other people have trouble doing most or all of their daily activities, including work and the basic chores of daily living. They may have to carefully plan how to best use their energy.
• People who are most severely affected by CFS may have difficulty getting out of bed and may require help with basic activities such as dressing, eating, and bathing.