**4.5 Shift work sleep-wake disorder (SWD)**

The mechanism behind SWD is thought to be governed by disruptions of 2 physiologic processes [1–3]. The first is related to one's homeostatic drive for sleep, which increases throughout wakefulness. The second is one's intrinsic rhythmic oscillations for sleep and wake periods, which is governed by the circadian pacemaker. This latter process is calibrated by environmental clues such as light. Both the homeostatic process and the circadian process are disrupted in SWD.

Individuals at greatest risk for SWD are those that work rotating night shifts, rather than permanent night shifts, because they are never able to adapt to a stable sleep–wake pattern [8]. In addition, those with other sleep comorbidities can have synergistic effects of sleep disturbance, which lead to symptomatic worsening.
