The grogginess and disorientation associated with waking up in the morning is referred to as sleep inertia. Sleep inertia is important because it can affect the performance of people who are required to work immediately upon waking up, such as physicians and truck drivers.

A new study, which appeared in the January 11, 2006 issue of the Journal of the American Medical Association , compared the effects of sleep inertia with sleep deprivation (lack of sleep) on cognitive (mental) performance. Researchers found that sleep inertia was associated with significantly worse performance than sleep deprivation.

About the Study

This study included nine paid volunteers with no medical, psychiatric, or sleep disorders. During the three weeks before the study, the participants were free of medications, alcohol, nicotine, recreational drugs, and caffeine, and maintained sleep schedules of eight hours per night. The study took place in a sleep laboratory. The participants slept eight hours per night for the first six days, followed by a 26-hour period of sleep deprivation. To measure their cognitive performance, the participants took standardized tests that required them to add pairs of two-digit numbers. The tests were designed to measure short-term memory, counting skills, and speed of cognitive processing. They took the tests throughout the first six days, and 1, 21, 41, 61, and 120 minutes after awakening, and every 2 hours on the sleep deprivation day.

Cognitive performance immediately upon wakening was 65% of peak performance, which was significantly worse than all other measurement points during the 26-hour sleep deprivation period. Between 21 and 61 minutes of wakefulness, cognitive performance ranged from 83% to 86%, and did not significantly change throughout the sleep deprivation period.

This study is limited by its small study size. A larger study would produce more reliable results.

How Does This Affect You?

These findings suggest that during the first minutes after awakening from a deep sleep, cognitive performance may be severely impaired. Since there is evidence that sleep deprivation results in cognitive impairments similar to those due to alcohol intoxication, the effects of sleep inertia on cognitive function may be more severe than the effects of alcohol.

Previous research has reported severe performance impairments lasting up to 10 minutes following awakening, with suboptimal performance detectable for up to two hours. This is especially important for people who are required to do their job immediately upon waking, such as medical professionals, firefighters, commercial truck drivers, and pilots. If you have something important to do that requires your full attention when you wake up, consider setting your alarm clock earlier. Losing a little sleep appears to be better than trying to perform at your best during the mental haze of early morning.