Sleepiness, Fatigue, and Sleep Disorders

Sleepiness and fatigue are terms used interchangeably, but they are different concepts. For example, a person who runs up 15 flights of stairs may feel fatigued when reaching the top but would not inevitably fall asleep following the exercise. On the other hand, sleepiness is characterized by a tendency to doze off during work or while sitting idle. Establishing the underlying cause for sleepiness can be a challenging feat. Sleep disorders such as sleep-disordered breathing (e.g., obstructive sleep apnea), hypersomnias (e.g., narcolepsy), circadian rhythm disorders, restless legs syndrome, and periodic limb movement disorder have been shown to cause excessive sleepiness besides insufficient sleep-acute or chronic. In many situations, sleepiness as well as ability to stay awake needs to be ascertained. This can be measured using a multiple sleep latency test or maintenance of wakefulness test. Present chapter focuses on the etiological factors, clinical presentation, and laboratory assessment of conditions leading to fatigue and sleepiness.