INTEGRATIVE CONCEPTUAL REVIEW Sleepiness at Work: A Review and Framework of How the Physiology of Sleepiness Impacts the Workplace Heather M. Mullins and Jose M. Cortina George Mason University Christopher L. Drake Sleep Disorders and Research Center, Henry Ford Hospital, Detroit, Michigan Reeshad S. Dalal George Mason University Sleepiness, the biological drive to sleep, is an important construct for the organizational sciences. This physiological phenomenon has received very little attention in the organizational science literature in spite of the fact that it influences a wide variety of workplace behaviors. In this article, we develop a framework through which sleepiness can be fruitfully studied. We describe (a) what sleepiness is and how it can be differentiated conceptually from related concepts such as fatigue, (b) the physiological basis of sleepiness, (c) cognitive and affective mechanisms that transmit the effects of sleepiness, and (d) the behavioral manifestations of sleepiness in the workplace. We also describe (e) job demand charac- teristics that are antecedents of sleepiness and (f) individual differences that moderate the aforementioned relationships. Keywords: sleepiness, job performance, job demands, affect, physiology Workplace psychology has expanded its focus to include re- search aimed at understanding the impact of nonwork variables on workplace outcomes. One area of particular interest is the role of sleep in workplace outcomes. Most people spend the majority of their time as adults either working (7 hr/weekday, 2 hr/week- end day; Basner et al., 2007) or sleeping (6.68 hr/night; Barnes, Wagner, & Ghumman, 2012). Despite the significant amount of time people spend engaging in these two activities, organizational psychologists know very little about the relationship between them. Sleep is inherently a physiological phenomenon. Thus, when one is studying the relationship between sleep and work variables, physiology provides useful models with which to examine con- nections among such variables. The approach taken in the present article is similar to that adopted by previous influential articles that have used a physiological framework in order to explain relation- ships among workplace variables. For example, Heaphy and Dut- ton (2008) used a physiological framework to explain the role of social interactions on physical health and work engagement. Schaubroeck and Ganster (1993) used a physiological framework to explain connections between work demands on experienced stress. Several other articles in the organizational sciences also have drawn from physiology to explain workplace phenomena (see Canli, 2004; Dimotakis, Conlon, & Ilies, 2012; Watson, Wiese, Vaidya, & Tellegen, 1999). With the present article, we hope to follow in this tradition by using this integrated approach. Specif- ically, we utilize a physiological framework to explain how changes that occur within the brain—in conjunction with sleep– wake processes—in turn influence workplace outcomes. That is, we demonstrate how these physiological changes inherently tied to sleep and wakefulness are ultimately responsible for changes in performance and other important workplace outcomes. Sleep research has shown that sleep problems are quite common. According to the 2008 Sleep in America Poll, at least 65% of people experience sleep problems a few nights a week (Swanson et al., 2011). Moreover, this research has shown that sleep problems including voluntary sleep restriction are linked to the nature of one’s employment, and full-time workers seem to be at greatest risk. The amount of sleep that full-time workers get has been decreasing over the past 30 years as the number of hours worked has increased (Knutson, Van Cauter, Rathouz, DeLeire, & Lauderdale, 2010). Furthermore, full-time workers are more likely than part-time workers to be at risk for sleep disorders and are more likely to report having driven while drowsy in the recent past (Swanson et al., 2011). Individuals who curtail the number of hours that they sleep are using the extra time for personal activities (Basner & Dinges, 2009; Basner et al., 2007; Biddle & Hamermesh, 1990), including Heather M. Mullins and Jose M. Cortina, Department of Psychology, George Mason University; Christopher L. Drake, Sleep Disorders and Research Center, Henry Ford Hospital, Detroit, Michigan; Reeshad S. Dalal, Department of Psychology, George Mason University. The authors would like to thank Tom Roth for his many insightful comments throughout the development of this article. Correspondence concerning this article should be addressed to Heather M. Mullins, Department of Psychology, George Mason University, 4400 University Drive, 3F5, Fairfax, VA 22030. E-mail: hmullin1@gmu.edu This document is copyrighted by the American Psychological Association or one of its allied publishers. This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. Journal of Applied Psychology © 2014 American Psychological Association 2014, Vol. 99, No. 6, 1096 –1112 0021-9010/14/$12.00 http://dx.doi.org/10.1037/a0037885 1096