Can naps cause sleep inertia?
Yes, especially longer naps. Short naps of about 10–20 minutes usually leave little grogginess, while longer naps are more likely to reach deep sleep and leave you foggy for a while after you wake up.
Nap length matters
In lab studies reviewed by Hilditch and McHill (2019), a 10-minute nap improved performance right away, while after a 30-minute nap the benefit only showed up once the grogginess had worn off, from about 35 minutes after waking. In general, the longer the nap, the more likely you are to wake from deep sleep and feel groggy.
Best nap timing
Early afternoon lines up with the natural post-lunch dip in alertness. Napping late in the day can make it harder to fall asleep at night.
Caffeine nap trick
Drink a coffee, then take a short nap of about 20 minutes. Studies in the same review found that caffeine taken just before a short nap reduced the grogginess afterwards.
Sources
- Hilditch & McHill, Nature and Science of Sleep, 2019. Sleep inertia: current insights
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