What is the primary symptom of Chronic Fatigue Syndrome (CFS)?

The primary symptom of Chronic Fatigue Syndrome (CFS) is persistent fatigue lasting at least six months that is not alleviated by rest. This distinguishing characteristic sets CFS apart from regular fatigue or temporary exhaustion. Individuals with CFS often experience debilitating exhaustion that significantly interferes with daily activities and does not improve with rest or sleep. This symptom can also be exacerbated by physical or mental activity, leading to a cycle of fatigue that is challenging to break.

While other options mention symptoms like severe headaches, joint pain, or insomnia, these are secondary symptoms that may accompany CFS but do not define the condition. The persistent, unyielding nature of the fatigue is what is primarily recognized in diagnoses and research related to CFS, emphasizing the importance of understanding this specific manifestation of the condition.