What is fatigue?

At the risk of stating the obvious, the most common cause of fatigue is getting too little sleep.

Fatigue is defined by lack of energy or a sensation of tiredness that may improve with rest. While it is a prominent symptom of numerous disorders – such as cardiovascular and endocrinal disease, anxiety and depression, and neurological disorders (multiple sclerosis) – fatigue is most often a result of not enough sleep and/or a sleep disorder.