Sleep accounts for one-third of our lives and is a crucial determinant of human performance. Lack of sleep is a threat to the nation's public health as it is linked to numerous chronic conditions, including type 2 diabetes, heart disease, obesity and depression (Fernandez-Mendoza & Vgontzas, 2013). Inadequate sleep is associated with elevated risks of vehicle crashes, workplace accidents and mortality (Cappuccio, D'Elia, Strazzullo, & Miller, 2010; Leger et al., 2014). Moreover, sleep is an important determinant of productivity and economic outcomes: one additional hour of sleep is associated with an increase in wages by 16% (Gibson & Shrader, 2014). Insomnia, a common sleep disorder, is characterized as difficulty with initiating or maintaining sleep, resulting in the disturbance of daytime functioning (Sateia, 2014). From 1993 to 2007, the number of office-based physician visits that involved complaints of sleeplessness and the number of visits that resulted in a diagnosis of insomnia increased 2-fold and 7-fold, respectively (Moloney, Konrad, & Zimmer, 2011). The prevalence of insomnia varies due to inconsistent diagnostic criteria, but the condition generally affects 10% to 34% of the population (Ellis,