The intriguing processes of sleep and dreaming have attracted attention from philosophers and artists for centuries, if not millennia. However, only in the past few decades has sleep medicine emerged as a credible and important scientific discipline worthy of attention both clinically and from research perspectives. Even now, it occupies a ‘Cinderella’ position within medical practice, despite increasing evidence that a disturbed sleep–wake cycle can directly damage physical, mental and emotional well-being. It is also clear that there is a circular relationship between sleep disruption and many ‘sleep toxins’, such as pain and disturbed mental health, which are, in turn, exaggerated by any resulting sleep deprivation. For example, insomnia may precipitate depression, anxiety or even psychosis rather than simply acting as a comorbid marker. Obesity, raised inflammatory markers and impaired cognition are further examples of common problems inextricably linked with chronically abnormal sleep (see Box 15.1 for proposed adverse effects of sleep disruption).

Paradoxically, the low profile of sleep disorders in medical education seems particularly apparent in psychiatry. Hopefully, this is changing. Most clinicians and, indeed, members of the public generally appreciate the importance of good-quality sleep, although the majority have little more than a basic understanding of its neurobiology. This chapter gives a broad outline of sleep and its disorders, with particular emphasis on those aspects germane to neuropsychiatry.

Normal v. abnormal sleep

Advances in our understanding of the neurobiology of sleep have challenged the traditional view that sleep is a passive or necessarily restful process. By contrast, rather than simply reflecting the absence of wakefulness, sleep is actively orchestrated with a highly reproducible and complex internal architecture (Frank, 2006). A typical pattern seen in a healthy adult is shown in Fig. 15.1. Episodes of rapid eye movement (REM) and nonrapid eye movement (non-REM) sleep recur through the night in four or five discrete cycles.