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 disorder.
[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.