An unusual circadian rhythm in an active duty service member

The case of a 29-year-old active duty US Navy sailor with severe sleepiness is presented. He was diagnosed with mild obstructive sleep apnea which did not fully explain his sleepiness. At follow-up, positive airway pressure usage demonstrated a progressive, variable phase delay. His sleep periods aligned with his 5-h on/10-h off (5/ 10) military duty schedule. Treatment with bright light exposure and melatonin resolved his circadian arrhythmia. While it is known that military personnel are habitual shift workers who receive insufficient sleep, there is little documentation of shift work disorders in this population.