Why do we sometimes feel sleepy as we wake up? Why is it sometimes harder to get active in the morning? In the present study, we investigated the determinants of subjective sleepiness upon awakening (546 awakenings) in 20 healthy subjects who were recorded with high-density electroencephalography (EEG). Surprisingly, we found that subjective sleepiness was higher upon awakening from REM sleep as compared to NREM sleep, even when adjusting for time spent asleep before the awakening. Sleepiness at awakening correlated with subjective sleep depth before the awakening and was highest when subjects did not report conscious experiences. At the EEG level, we found that awakenings from both REM and NREM sleep were characterized by the persistence of ‘sleep-like’ low-frequency activity (delta and theta power) in posterior brain regions. Furthermore, subjective sleepiness negatively correlated with high-frequency activity and positively with low-frequency activity immediately after awakening. The effect of ‘EEG activation’ was not localized, but rather diffuse. These results challenge the common assumption that subjective sleepiness is strongest upon awakening from ‘deep’ slow wave sleep. They also suggest that the awakening process displays distinctive regional activity patterns, with anterior and central brain regions ‘waking up’ before posterior regions. Finally, these results provide an objective correlate of subjective sleepiness.