Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overworking, stress, lack of exercise, improper nutrition, drug abuse, boredom, or a symptom of an underlying illness or a disorder. It may also be a side-effect of medication or caused by an interaction between medications or medication(s) and alcohol. It may also be an altered level of consciousness.[1]
When part of a normal response, lethargy often resolves with rest, adequate sleep, decreased stress, physical exercise, and good nutrition.[2] Lethargy's symptoms however can last days or even months,[3] so it can be a sign of a recent underlying illness or infection if it doesn't resolve normally.
^Tindall, Suzie C. (1990), Walker, H. Kenneth; Hall, W. Dallas; Hurst, J. Willis (eds.), "Level of Consciousness", Clinical Methods: The History, Physical, and Laboratory Examinations (3rd ed.), Boston: Butterworths, ISBN978-0-409-90077-4, PMID21250221, retrieved 2022-03-26
^Hall J. E., Guyton A. C. (2006): Textbook of medical physiology, 11th edition. Elsevier Saunders, St. Louis, Mo, ISBN0-7216-0240-1.
The dictionary definition of lethargy at Wiktionary