A lethargic definition is described as feelings of tiredness, fatigue or lack of energy that can be accompanied by depression, decreased motivation or apathy. The meaning of lethargic is the same as somnolence which is defined as a state of near sleep, a strong desire to sleep or sleeping for longer periods (hypersomnia). Feeling tired and lethargic can be a normal reaction to; not getting enough sleep, overexertion, overworking, stress, lack of exercise and boredom. If lethargy is caused by a normal reaction it is usually resolved with decreased stress, good diet and getting enough sleep. Read more »