Waking up is not instantaneous but gradual (sleep inertia): the prefrontal cortex remains sluggish for about 15 minutes, leading to a temporary mental fog that is sometimes worse than that of a sleepless night, a phenomenon of confusional arousal that affects one in seven adults.

noli's read

The idea of gradual awakening is well-supported by the science of sleep inertia. A brain imaging study (Balkin et al., 2002) shows that while deep brain regions activate quickly, the prefrontal cortex—our center for attention and decision-making—takes 5 to 30 minutes to regain its normal blood flow. Regarding performance, a behavioral study (Wertz et al., 2006, JAMA) confirms that cognitive abilities immediately after waking are temporarily more impaired than after a full night of sleep deprivation. Finally, the proportion of one in seven adults is taken from a large observational study from Stanford University (Ohayon et al., 2014, Neurology) evaluating the frequency of confusional arousals, commonly known as "sleep drunkenness." This post is therefore based on extremely robust scientific data.

the sources

No named source held this one up — that absence is part of the verdict.