The meaning of fatigue is extreme tiredness resulting from mental or physical exertion or illness. The cause of chronic fatigue is still unknown. Some people may be born with a predisposition for the disorder, which is then triggered by a combination of factors. Potential triggers include: Viral infections. Because some people develop chronic fatigue syndrome after having a viral infection, researchers question whether some viruses might trigger the disorder. Suspicious viruses include the Epstein-Barr virus, human herpes virus 6. No conclusive link has yet been found. Immune system problems. The immune systems of people who have chronic fatigue syndrome appear to be impaired slightly, but it's unclear if this impairment is enough to actually cause the disorder. Hormonal imbalances. People who have chronic fatigue syndrome also sometimes experience abnormal blood levels of hormones produced in the hypothalamus, pituitary glands or adrenal glands. But the significance of these abnormalities is still unknown. Physical or emotional trauma. Some people report that they experienced an injury, surgery or significant emotional stress shortly before their symptoms began.