Polysomnogram (PSG) is a multi-channel ("poly") recoring ("gram") during sleep ("somno"), resulting from a sleep test, polysomnography. A doctor may order a polysomnogram because the patient has a complaint such as daytime fatigue or sleepiness that may be from interrupted sleep. Typically, doctors order a polysomnogram to diagnose or rule out obstructive sleep apnea. Although the PSG can be done during the day or night, the vast majority of sleep studies are done at night, when most people sleep. Shift workers and people with circadian rhythm sleep disorders can be accommodated in some labs by having the test at other times of day.