Newly awake more groggy than sleep-deprived: study

"For a short period, at least, the effects of sleep inertia may be as bad as or worse than being legally drunk," said researcher Kenneth Wright of the University of Colorado at Boulder.

That befuddled feeling usually lasts for at least a few minutes but may be detectable for up to two hours, Wright wrote in a report published in this week's issue of the Journal of the American Medical Association.

The findings are relevant to emergency workers such as firefighters, or for truck drivers and resident doctors who must spring into action after awakening from naps. A groggy driver is accident-prone, and a hazy doctor might make a mistake calculating a drug dosage, the report said.

Wright's study of 16 subjects found the most severe impairments were evident on performance tests taken during the first three minutes after awakening from an eight-hour sleep.

"We found the cognitive skills of test subjects were worse upon awakening than after extended sleep deprivation," he said.

There is evidence that the cortical areas of the brain thought to be responsible for problem-solving, complex thought and emotions take longer to wake up than other parts of the brain, Wright wrote.