ABSTRACT
Of the various human experiences that can be considered universal, ‘sleepiness’ is among the most difficult to define precisely. In part, this may be because sleepiness is a hypothetical construct that encompasses a panoply of changes in mental abilities, mood, motivation, subjective experience, and physiology that reflect the need for sleep – while the ultimate purpose of sleep itself remains elusive. In the present chapter, current concepts regarding the relationship between inadequate sleep duration and sleepiness are described and discussed.
