Insomnia and Its Correlates: Current Concepts, Epidemiology, Pathophysiology and Future Remarks

Insomnia is a common sleep disorder. People suffering from insomnia generally report not only sleep-related symptoms such as difficulty initiating, maintaining, obtaining sufficient restorative sleep, but also experience various daytime impairment reflective of sleep deficits (Buysse, 2008; Riemann et al., 2011). The generic term “insomnia” as a diagnostic entity is defined as a complaint of sleep problems coupled with impairment of daytime functioning, including reduced alertness, fatigue, exhaustion, dysphoria and other symptoms. The complaints have to endure for at least 4 weeks to be diagnosed as insomnia, according to the current diagnostic classification manual (Abe & Mishima, 2008).