Have you heard of ‘sleep inertia’? It’s that horrible groggy feeling we sometimes get when we first wake up. It is especially strong when you are woken from a deep sleep by a noise, interruption or an alarm. However, is it a bad sign? Should we be worried about sleep inertia? And, can we do anything to reduce it?
In this blog, Dr Lindsay Browning explains exactly what sleep inertia is, why we feel groggy and what we can do to reduce it. Take a read.
What is sleep inertia?
Sleep inertia is the groggy feeling when somebody wakes up from a deeper part of sleep, and the body is still transitioning from sleep to wake. This often means they don’t feel fully alert and awake yet.
If you wake up from a deeper part of sleep, particularly slow-wave sleep, you are more likely to experience sleep inertia. If you wake up from a much lighter part of sleep, typically at the beginning or end of a sleep cycle, you are less likely to experience as much sleep inertia. Also, if you set your alarm for a different wake-up time from your usual one, either earlier or later, you might find yourself waking from a deeper part of sleep and, therefore, experience more sleep inertia.
What makes a person more likely to experience sleep inertia?
As well as where you are in the sleep cycle, if you are jetlagged or need to wake up at a significantly different time to usual (such as if you have to wake early at 3 am for a flight) you are more likely to experience sleep inertia. This is because our sleep cycles tend to have more deep, slow-wave sleep in the first half of the night and sleep tends to get lighter and less deep with each subsequent sleep cycle towards the morning. Therefore, if you wake up when your body clock thinks you should still be in the middle of your night’s sleep, you are more likely to wake up from a deeper part of sleep and experience sleep inertia.
Is sleep enertia a bad thing or a sign you haven’t had enough sleep? Could it be a sign of a deeper sleep disorder?
It is important to remember that sleep inertia is not bad. In fact, it’s completely normal. Making sure that you get enough sleep is more important than worrying about avoiding sleep inertia, because even if you wake up with sleep inertia, it will usually wear off fairly quickly.
If you find that you experience severe sleep inertia most mornings, or it doesn’t shift after waking and the sleepiness and grogginess persists long into the day, then this might be a sign that you aren’t getting enough sleep. You might have circadian misalignment, or you might possibly have another sleep disorder such as sleep apnoea. If this is the case, it’s best to talk to your GP and a sleep specialist.
How can I reduce that groggy feeling when waking up to an alarm?
Natural daylight
Natural daylight exposure (with the rising sun in the morning) may help to reduce sleep inertia since, even through closed eyelids, you can sense the sunlight increasing, which has been suggested to help pull you from a deeper part of sleep into a lighter part of sleep. Additionally, you can open your curtains as soon as you wake up to let bright light into your bedroom, which can help to shift sleep inertia more quickly.
In addition, actually getting outside and seeing natural daylight soon after waking is one of the best ways of helping you feel more alert more quickly. You can buy gadgets to help with this, such as blue-light-enriched glasses, but, at the end of the day, natural daylight is easy, free and one of the most effective practical options for most people.
Consistent wake up times
Having a consistent wake time can help your body get used to that time as wake-up time. This helps your body shift to that being a more natural waking point between sleep cycles, rather than from a deeper part of sleep.
Using sleeping trackers – pros and cons
There are some sleep tracking apps that can help to predict when you are likely to be in a lighter part of sleep compared to in a deeper part of sleep, and they can adapt your morning alarm accordingly. However, I am not a big fan of these devices because they are not necessarily very accurate at predicting sleep stages compared to gold-standard polysomnography, and they may work by waking you up earlier and therefore shortening the amount of sleep you get. As getting 7 to 9 hours of sleep regularly is so important for our health and wellbeing, I would not want to advise people to sacrifice sleep so that they can avoid sleep inertia when sleep inertia usually dissipates fairly quickly after waking. Whereas, short sleep can have a greater negative impact on physical and mental wellbeing.
Does ‘sleeping in’ at the weekend impact our level of sleep inertia on Monday mornings?
Sleeping in later at weekends can shift your sleep-wake schedule later, making a Monday morning alarm feel more like waking up during your “biological night” . This effect may be more pronounced in naturally later chronotypes (owls) compared to earlier chronotypes (larks). 
What else makes sleep inertia worse?
There isn’t anything you can do to immediately flip your brain from sleepy to alert, however, staying in bed repeatedly pressing snooze is unlikely to help you quickly wake up. It’s much better to get up, move around and get the curtains open/access daylight.
Is a sunrise alarm clock a good idea for helping people to wake up in a lighter part of their sleep cycle?
I am a great fan of sunrise alarm clocks, especially for people who struggle in the morning to wake up. People who tend to be evening-type chronotypes (owls) often have the most difficulty waking up feeling refreshed in the morning, in which case getting bright light exposure soon after waking can be really helpful. Also, as sunrise alarm clocks introduce gradually increasing light before waking, which your eyes may sense through closed eyelids, this can help make the transition from sleep to wake gentler and more gradual. If you can’t afford a sunrise alarm clock, because they are quite expensive, then opening your curtains as soon as you wake and going outside soon after waking up can be very helpful too and is free. 
Worried about sleep inertia or feeling groggy consistently?
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