What causes chronic fatigue even after a full night's sleep?

Chronic fatigue despite adequate sleep often stems from poor sleep quality rather than insufficient duration. Conditions like sleep apnea interrupt restorative deep sleep cycles without the person fully waking, leaving them exhausted. Other common causes include hypothyroidism, anemia, diabetes, and depression, all of which disrupt cellular energy production or neurological function. Lifestyle factors also play a role, including chronic stress, poor diet, sedentary behavior, and dehydration. Autoimmune conditions like lupus or fibromyalgia cause persistent fatigue as the immune system stays in a heightened state. Viral infections can trigger post-viral fatigue syndromes, as seen with conditions like ME/CFS. A doctor can run blood tests to identify underlying causes and guide appropriate treatment.