If you’ve ever felt groggy after waking up, you’ve experienced sleep inertia. It usually lasts 30 to 60 minutes but can affect you longer if you’re sleep-deprived. Other symptoms include disorientation, grumpiness, impaired short-term memory, reduced decision-making performance, and slower reaction time.
For many people, sleep inertia is a minor inconvenience. It just means taking a little extra time to wake up before doing something that requires their full attention. But it can be a big problem for people who may have to perform critical tasks as soon as their eyes snap open, such as military personnel.
Causes of sleep inertia
You might guess that being tired would be a cause of sleep inertia. If so, you’d be right.
As you use energy, your brain releases a substance called adenosine that makes you feel the need to sleep. Sleeping refreshes you in part because your brain clears out your adenosine as you sleep. So, if your adenosine isn’t cleared out when you wake up, you may experience sleep inertia.
In a 2019 review of sleep inertia studies, researchers observed that not getting eight hours of uninterrupted sleep increases sleep inertia symptoms. Being awake for a long time before sleeping and not sleeping well over a several-day period can also lead to increased symptoms. This may be because all those things don’t give your brain enough time to clear out your adenosine as you sleep.
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Going against your circadian rhythms, the internal processes that tell your body to sleep at night and wake up in the morning, also may cause sleep inertia. The decreased cognitive ability associated with sleep inertia is most pronounced when people are awakened in the middle of what their bodies consider to be night.
Additionally, slow blood flow in your brain may help cause sleep inertia. The 2019 review cited a study suggesting that it takes about a half hour after waking for blood flow in the brain to reach its pre-sleeping speed.
Dealing with sleep inertia
There are two overall ways to deal with sleep inertia. You can take steps before you go to sleep to minimize its effect on you after you wake up, and/or you can take steps after you wake up to shake it off more quickly.
Caffeine can be involved in both. It blocks the adenosine receptors in your brain, which reduces adenosine’s ability to make you sleepy.
That’s why, if you want to get a good night’s sleep, you shouldn’t have anything with caffeine in it less than six hours before turning in. Otherwise, the caffeine may prevent the adenosine in your brain from making you feel tired.
Similarly, one way to help yourself wake up is to drink a cup of caffeinated coffee. The caffeine in it can stop residual adenosine from making you groggy. The problem with this strategy is that caffeine takes about a half hour to affect you, and your sleep inertia may have ended by then anyway.
The delayed effect of caffeine can come in handy if you drink some coffee before a quick nap, however. If you snooze for 30 minutes, the caffeine will be kicking in when you awake, so you may not experience sleep inertia at all. This can be a good strategy for hospital workers on night shifts to follow.
Other than consuming caffeine, nothing you can do after waking to minimize sleep inertia has been shown to work consistently, according to a 2016 review of sleep inertia studies. This suggests that you should focus on trying to sleep well to minimize how often and strongly you experience sleep inertia.
Strategies for sleeping well include maintaining a regular sleep schedule, keeping your bedroom cool and dark, and avoiding nicotine and alcohol (as well as caffeine) before bed. These healthy sleep habits will not only help fend off the symptoms of sleep inertia. Getting enough sleep can also improve your mood, strengthen your immune system, help you maintain a healthy weight, and lower your risk of developing serious health issues.