Lethargy is a state of tiredness, sleepiness, weariness,fatigue, sluggishness, or lack of energy. It can be accompanied bydepression, decreased motivation, orapathy. 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 disorder. It may also be a side effect of medication or caused by an interaction between medications andalcohol. It may also be analtered 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] Its symptoms, however, can last days or even months,[3] so it can be a sign of a recent underlying illness or infection if it does not resolve normally.
The dictionary definition oflethargy at Wiktionary