Waking up unrefreshed? Blame your night out. According to British researchers, drinking alcohol before bed decreases your quality of sleep.
After reviewing 153 studies on alcohol and sleep, researchers narrowed in on 27 of the best. Their findings: After a big night of drinking (equivalent to four or more beers), your entire sleep cycle is disrupted—you spend more time awake, have fewer dreams, and have an elevated heart rate.
What’s going on? On a sober night, you cycle between deep sleep—when your body heals itself—and Rapid Eye Movement (REM) sleep, where your brain de-frags itself like a hard-drive for the day ahead.
But when you’re drunk, you don’t get the REM (dreaming) sleep you need.
What’s more: While alcohol depresses your nervous system, helping you fall asleep faster and sleep more soundly at the start of the night, it revs your body in the second half of the night.
Your body never shuts down your sympathetic nervous system—which keeps you alert during the day—like it’s supposed to. The result: As soon as the sleep-inducing effects of the drug wear off, your active sympathetic nervous system wakes you up.
To see exactly what’s happening, join us on a journey through your drunk sleep.
1 a.m.: After a long night of boozing, you hit the bed.
What’s happening: You fall asleep faster, says lead study author Irshaad Ebrahim, MBChB, MRCPsych, of the London Sleep Centre.
Because drinking depresses your brain, you’re zonked out for 4 to 16 minutes sooner than you otherwise would be. And you enter deep sleep—the dream-free kind—about 8 minutes sooner, too.
The only problem: Your heart rate is elevated 9 beats per minute, meaning that parts of your nervous system are still more active than they should be, spelling trouble for later.
2 a.m.: You still have your shoes on.
What’s happening: The alcohol is keeping you sedated, so your sleep is uninterrupted, says Ebrahim. You’re not dreaming, you’re not stirring.
You’re out cold, but your heart rate is elevated by 13 beats. For someone who’s trying to get some rest, your body is actually pretty active.
3 a.m.: You’re snoozing like a baby.
What’s happening: Alcohol delays the onset of REM sleep, says Sonu Ahluwalia, M.D., Clinical Chief of Orthopedic Surgery at Cedars Sinai Medical Center.
Not only does it come on later, but you get up to 9 percent less REM sleep during the first half of the night than you should be. The result: You’re left feeling groggy in the morning.
5 a.m.: You’re under the covers.
What’s happening: You’re no longer in deep sleep, says Ebrahim. And as the alcohol wears off, your sympathetic nervous system—which wasn’t shut down because of all the drinking—kicks in, says Seiji Nishino, Ph.D., a professor of psychiatry at Stanford University.
As a result, you start waking up—about 17 percent more frequently than you should be throughout the second half of the night, according to a 2012 study by Japanese researchers.
6 a.m.: You’re restlessly dreaming.
What’s happening: By now, your body has metabolized much of the alcohol and you’re feeling wakeful without its depressive effects, says Dr. Ahluwalia.
You’re tossing and turning, and waking up without knowing it—spending 4.39 percent more time awake throughout the second half of the night.
Your heart rate is elevated by 11 beats, and you know it’s going to be a long day ahead.
8 am.: Fine, fine, you’re awake!
What’s happening: You want to keep sleeping, but your sympathetic nervous system is pushing you up, and the alcohol has worn off.
As a result, you get the last thing in the world that you want: an early wake-up, says Ebrahim.
And because you’ve missed out on much of your REM sleep, you wake up feeling gross and tired, Dr. Ahluwalia says.