Easy fatigue can reflect low fitness and sleep debt, but it may also signal anemia (iron deficiency), thyroid disorders, heart/lung issues, post-infection recovery, chronic inflammation, or mental health strain. Clues matter: exertional shortness of breath/palpitations suggest cardiopulmonary causes; unrefreshing sleep and snoring suggest sleep disorders; heavy bleeding suggests iron deficiency; cold intolerance/constipation/weight gain may point to hypothyroidism. If it persists or worsens, a clinical assessment with targeted labs is appropriate.