Possible causes can include physical or emotional trauma.
One hypothesis suggests that the disorder may be associated with changes in craniofacial and skeletal muscle metabolism, such as decreased blood flow, which could cause chronic fatigue and weakness. Another hypothesis is that an infectious microbe, such as a virus, triggers the illness. At this point, no virus or microbe has been identified. Pilot studies have shown a possible inherited tendency toward the disease. The disorder has an increased frequency among women 20 to 50 years old.