Sleep hygiene can be defined as controlling "all behavioural and environmental factors that precede sleep and may interfere with sleep." It is the practice of following guidelines in an attempt to ensure more restful, effective sleep which can promote daytime alertness and help treat or avoid certain kinds of sleep disorders. Trouble sleeping and daytime sleepiness can be indications of poor sleep hygiene. The International Classification of Sleep Disorders-Revised (ICSD-R) states on page 75: "The importance of assessing the contribution of inadequate sleep hygiene in maintaining a preexisting sleep disturbance cannot be overemphasized."
Doctors and clinics which advise sleep hygiene for patients and families have lists of suggestions which may include advice about timing of sleep and food intake in relationship to it, exercise, sleeping environment etc. Which items are suggested for which patients are selected by the clinician, depending on knowledge of the individual situation; the counselling is presented as a form of patient education. Re-education involves a combination of advice about homeostatic, adaptive and circadian aspects of sleep control, how to avoid sleep deprivation, and how to respond to unwanted awakenings from sleep if these occur. As the second edition of the ICSD (ICSD2, 2005) points out, the "sleep disruptive effects of poor sleep hygiene are often obvious to others, but the patients show little insight into this fact."