gy, difficulty concentrating and irritability (Walsh & Others, 1999, p. 3029).
This, however, is still a general definition, for insomnia may involve either the quality or quantity of sleep (or both), and it may have its source in one or more physiological, neurological, or psychological causes that operate singly or overlap and converge. According to Walsh, et al., who initially published findings as a report from the Working Group On Insomnia of the National Heart, Lung, And Blood Institute of the National Institutes of Health (1998) and later published them in the professional literature (1999), insomnia may be acute (temporary, lasting up to several weeks), or chronic (occurring three nights or more per week for more than four weeks). Acute insomnia is also sometimes described as situational insomnia, connected to a specific stressful life event, but lasting three weeks or less (Berliner, 1999). Such events might include the illness or death of a loved one, or one's own illness.
Lack of sleep may also be associated with medication and substance use
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