Insomnia is a major public health hazard. Complexity of insomnia patho-physiology is intriguing and is an exciting subject of inquiry. The current article summarizes the recent developments in our understanding of insomnia. Although the early models of insomnia were unidirectional, they provided foundation for development of more integrative models. Sleep- wake regulation and more specifically conceptual understanding of sleep homeostasis, circadian influence, and hyperarousal further added new dimensions to our understanding of insomnia. However, there is more appreciation than ever of the fact that a lot more work must be done before even thinking about finding a conclusive evidence of what causes insomnia and what maintains it. Some of the legendary work is cited in the reference section to develop an understanding of intricate interplay of multiple systems within the body that cause sleep and lack of it.
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