Sleep Inertia = Grogginess

Do you wake up often groggy, without any sense of time or place? You can’t seem to think straight, movements are stiff, and you feel like you were stunned. This phenomenon is called sleep inertia or grogginess. Your motor and cognitive abilities are weakened temporarily. During sleep inertia, your senses are impaired, and focusing your thoughts is challenging.

Sleep inertia is typical, and it occurs in some form when waking up. Sleep inertia is the strongest immediately after waking up, and the symptoms fade away, usually in 15-60 minutes. However, the effects vary between individuals and days, and in some cases, the grogginess can last up to hours. Two factors are mainly affecting the intensity of sleep inertia: 

  1. Sleeping too little (or sleep debt that has not been slept off)

  2. Waking up at a wrong stage of your sleep cycle (during deep sleep)

If the grogginess continues to late morning and into the day time, there is a need for changes and careful checking the reasons behind your grogginess. During the next few lessons, we’ll look into the roots of what causes grogginess and sleepiness in the morning.

Additional Reading


Hilditch, C. J., Dorrian, J., & Banks, S. (2016). Time to wake up: Reactive countermeasures to sleep inertia. Industrial Health, 54(6), 528–541.

Tassi, P., & Muzet, A. (2000). Sleep inertia. Sleep Medicine Reviews, 4(4), 341–353.