Lethargy is a state of generalized fatigue or sluggishness, sometimes with decreased alertness.
It is normal to have periods of low energy when one needs to rest and recuperate. However, if low energy persists and a person continually feels sluggish, disinterested in life, and has low energy, the situation should be investigated by a physician. Depression is a common cause of lethargy, but there may be other medical problems causing low energy, such as low thyroid hormone.
A thorough evaluation by a physician is indicated for persistent lethargy. The treatment will depend on the underlying problem and the severity of the symptoms.
Lethargy worsens and leads to decreased responsiveness or if a person is difficult to arouse, unable to answer questions or does not know their name or where they are.