Lethargy is a state of physical or mental weariness, fatigue, sluggishness, or lack of energy. It can be accompanied by depression, decreased motivation, or apathy, but can also present with having a desire, but not the energy to initiate or perform tasks. 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 and alcohol. It may also be an altered level of consciousness.