ABSTRACT
Many disorders of the sleep–wake continuum lead to impaired daytime wakefulness with the possibility that cognition may be prejudiced. Sleepiness is not easy to define or to measure, but it is important to appreciate that the ability or the tendency to fall asleep quickly is not necessarily an indication of an undue generalized sleepiness that could impair the day-to-day life of the individual and imply sleep pathology. Subjective assessments are well established in the investigation of the sleep–wake continuum. The Stanford Sleepiness Scale incorporates questions dealing with activity, alertness, cognition and sleepiness. The maintenance of wakefulness and multiple sleep latency tests require electroencephalographic recordings, and so present logistic problems in routine clinical practice. Tests that involve the measurement of sleep latencies and the maintenance of wakefulness measure aspects of sleep propensity. Continuous positive airway pressure is the mainstay of treatment for obstructive sleep apnoea syndrome.
