Got a decent amount of sleep last night? Even so, your mental skills still might not have been all that sharp first thing this morning.

It’s that woozy time when your eyes are open, but you’re not exactly alert. All things being equal, you might rather roll over and hit the snooze button than put your feet on the floor and start the day. According to a new study, your brain's ability to function during those first waking moments may be as impaired as if you'd been drinking.

Sleep experts call that feeling “sleep inertia.” Everyone else calls it grogginess. Now, a small new study shows it’s far from your brain’s finest hour.

The brief report, published as a research letter in The Journal of the American Medical Association, comes from researchers including Kevin Wright, PhD, of the Sleep and Chronobiology Laboratory at the University of Colorado at Boulder.

“For a short period, at least, the effects of sleep inertia may be as bad as or worse than being legally drunk,” Wright says in a news release.

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Wright’s small study included eight men and one woman. They were about 29 years old, on average, and were paid for their participation.

None had sleep disorders. They also hadn’t recently crossed time zones or done shift work.

For three weeks, participants got eight hours of nightly sleep at home. They also avoided alcohol, medications, nicotine, recreational drugs, and caffeine during that time.

Next, participants spent a week at a sleep lab. For the first six nights, they got eight hours of sleep following their normal bedtimes.

During the days, participants spent some time adding double-digit numbers together. They weren’t just killing time. That adding skill was supposed to come in handy later on.

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After the sixth night at the lab, participants were woken up after eight hours of sleep. Immediately, they took an adding test.

There was no hemming and hawing, no dawdling over coffee or the newspaper. Instead, the day started abruptly, with the math test starting within seconds of waking.

Participants fumbled and stumbled through the test, performing much worse than usual. After about 20 minutes to an hour, their performance was closer to normal.

Then, participants were kept up for 26 hours straight at the lab. Right afterward, they took another addition test. Math scores were better after the all-nighter than immediately after eight hours of sleep.

“These were very healthy people who had performed the test hundreds of times, making the results even more profound,” Wright says in the news release.

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Grogginess Like Drunkenness

Other researchers have equated sleep inertia, or morning grogginess, to being drunk, write Wright and colleagues.

Many people can delay mental challenges for a few minutes while their brains get up to speed.

But some people, like doctors, soldiers, and emergency workers, have to be ready to go at a moment’s notice, Wright’s team notes.

The adding test challenged short-term memory, counting skills, and speedy thinking. The brain’s prefrontal cortex handles those skills, along with problem solving, complex thinking, and emotions.

In short, workers who must be at the top of their game at the drop of a hat can’t afford a groggy prefrontal cortex.

Sleep Dos & Don'ts

Give Me a Moment … or More?

Sleep inertia doesn’t last long, with “severe” performance problems lasting three minutes, write the researchers.

They note that in other studies, “severe” performance problems have lasted up to 10 minutes, with detectable glitches present for at least two hours after waking.

Their study was small, and people don’t normally do math first thing in the morning, so the researchers call for more studies of sleep inertia.

The goal: Learn how bad it really is and how to handle those morning moments when duty calls but the brain can’t quite keep up.

By Miranda Hitti, reviewed by Louise Chang, MD

SOURCES: Wertz, A. The Journal of the American Medical Association, Jan. 11, 2006; vol 295: pp 163-164 .News release, University of Colorado at Boulder.