Sleep inertia: symptoms, causes and treatment

October 16, 2020 4 mins read
Sleep inertia: symptoms, causes and treatment

Raise your hand if you’ve ever woken up in a groggy state, disorientated and still half asleep… this is what is known as sleep inertia, the not-awake-yet feeling that comes when you wake up during the deepest phase of your sleep cycle.

It’s a very common sleep experience, and there’s a ton of information available on why it happens, how it happens, and what you can do to prevent it. So let’s dive into the science of deep sleep and learn why waking up at the wrong time can cause this foggy feeling.

What is sleep inertia?

Sleep inertia refers to the transitional state between sleep and waking. According to the Sleep Council, sleep inertia happens when you wake up during slow-wave sleep. This is the phase during stages 3 and 4 of the sleep cycle which is most difficult from which to wake. Some essential functions occur during slow-wave sleep like the regeneration of tissue and cells and the strengthening of the immune system.

Now, upon waking up from slow-wave sleep, your prefrontal cortex (PFC), which has been left behind in dreamland, must catch up with the rest of your body. The PFC is responsible for decision making and self-control, so while your body waits for your brain to catch up, you’ll experience the groggy feeling of sleep inertia.

It’s important to note here, that while sleep inertia is a natural sleep phenomenon, there are instances in which it can be dangerous, such as in the case of healthcare workers or military personnel who wake abruptly in the night and are required to make cognitively-taxing decisions.


Because sleep inertia is a physiological state of diminished cognitive functioning and sensory-motor performance, you can expect to experience the following symptoms:

  • A heavy feeling after you wake up
  • Struggling to concentrate or focus
  • A foggy brain, grogginess and drowsiness

Typically, symptoms disappear after 30 minutes (or in some cases, 15 minutes), but scientists believe that full recovery takes between 1-2 hours.

What causes severe morning sleep inertia?

While there are three leading causes of sleep inertia, which all originate in the brain, sleep deprivation can also be to blame. This is because sleep deprivation increases the percentage of time you spend in slow-wave sleep and the chances of waking during this deep sleep phase.

These are the leading causes, according to scientists:

Higher levels of delta waves

Studies have shown that there are higher amounts of delta waves in people with sleep inertia. These delta waves are generated during deep sleep where healing and restorative functions of the body take place. Beta waves which are produced by the brain to give you a sense of being alert, are found in smaller quantities in people with sleep inertia.

Slower brain reactivation

Remember the prefrontal cortex (PFC)? During sleep inertia, it can take some time for it to begin fully functioning with all the regions of your brain that control your bodily functions and movements. Because it is in charge of your reasoning and self-control, the slow activation of the PFC leads to the disorientation and grogginess felt during sleep inertia.

Slow blood flow in the brain

From the time that you wake up and regain all your senses, there could be a delay in blood flowing to and reaching your brain. This lack of oxygenated blood circulation to the brain has also been found to be a cause of sleep inertia.

How long can sleep inertia last?

Sleep inertia can last for 5 to 30 minutes, but the effects can be felt for up to 4 hours. During that period, it’s likely you will feel unfocused and unable to be fully present.

How to prevent sleep inertia

There are five ways you can prevent sleep inertia.

  • Drinking coffee first thing in the morning will provide your system with a jolt of energy and wakefulness that will pick you up from a sleep inertia slump.
  • Scheduling a nap in the afternoon can also keep sleep inertia at bay. A snooze of 10 to 30 minutes will refresh you so you can offset any drowsiness you might feel.
  • Splashing your face with cold water upon waking is also a practical way to get yourself out of that sleep inertia haze.
  • Instead of pressing the snooze button, get up immediately and let natural sunlight in. Studies have found that the sooner you are exposed to light, the better, as your brain is effectively prodded into wake mode. Light also suppresses the production of the sleep hormone melatonin.

To optimize your bedtime, you can use a sleep calculator to align yourself with your sleep cycles. This way, you can get the benefit of all 5 sleep cycles without waking up during stages 3 and 4 when sleep inertia occurs.

Sleep inertia is preventable and manageable. By knowing what triggers it and quickly nipping that in the bud, it doesn’t have to spoil your day.