Shift Work Disorder Is A Sleep Disorder Caused By Your Work Schedule Requiring You To Stay Awake When Your Body Wants To Sleep. Then you have to try to go to sleep when your body expects you to be awake. The body has an internal clock called the Circadian Rhythm, which is set by light exposure. When this Rhythm is disrupted, many side effects can occur, including unrefreshed sleep, insomnia, drowsy driving, excessive sleepiness, and decreased alertness, resulting in poor job performance and an increased risk of accidents.