We're told fatigue is 'just stress, sleep more'. The truth is richer: cellular energy, the stress axis, thyroid, sleep architecture, silent inflammation. Five threads, and plenty of false fixes sold along the way. Level 1: what "I'm exhausted" actually covers. Level 2: the numbers that mislead — a "normal" ferritin at 15 µg/L, an in-range TSH, vitamin D measured out of season. Level 3: when fatigue points to something worth exploring with a doctor rather than one more supplement. Sources: WHO, NIH ODS, Cochrane. See our terms and conditions. The information shared here does not replace advice from a qualified health professional.