Different than drowsiness (a need to sleep), fatigue is characterized by a decreasing ability to exert oneself – a physical and mental lack of energy and motivation. Fatigue is usually associated with the feeling of being tired, bored, weak, and/or irritable.
Fatigue can occur at any time of day but occurs most often in the morning, many cases in as little as one hour after waking up. Some people will experience fatigue all day long.