Some facts about Fatigue

(From Medline Plus...)

Alternative Names Tiredness; Weariness; Exhaustion; Lethargy

Fatigue is a feeling of weariness, tiredness, or lack of energy.

Fatigue is different from drowsiness. In general, drowsiness is feeling the need to sleep, while fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of indifference or not caring about what happens) can be symptoms of fatigue.
Fatigue can be a normal and important response to physical exertion, emotional stress, boredom, or lack of sleep. However, it can also be a nonspecific sign of a more serious psychological or physical disorder. When fatigue is not relieved by enough sleep, good nutrition, or a low-stress environment, it should be evaluated by your doctor. Because fatigue is a common complaint, sometimes a potentially serious cause may be overlooked.
The pattern of fatigue may help your doctor determine its underlying cause. For example, if you wake up in the morning rested but rapidly develop fatigue with activity, you may have an ongoing physical condition like an underactive thyroid. On the other hand, if you wake up with a low level of energy and have fatigue that lasts throughout the day, you may be depressed.