Chronic fatigue syndrome (CFS) symptoms usually start suddenly. But for some people, they develop gradually over weeks or months. Symptoms can change in a day, and from day to day. They tend to stop (remission) and then start again (relapse).

These core symptoms are:

Extreme physical fatigue, mental fatigue, or both not relieved by rest Joint Pain Headache Low body temperature

Feeling unwell after being active Sleep problems Muscle Pain Worse with stress

It can be constant, or it can come and go. It is not relieved by rest. This fatigue also is so severe that it interferes with your work, your play, and your social activities.