(CNN)The alarm goes off and you shudder awake, unsure of where you are. Groggily you recognize your room and slowly roll out of bed thinking, "It can't be morning. Didn't I just go to bed?"
How to kick-start your brain in the morning (and no, we don't just mean coffee)
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Called sleep inertia, it happens when you suddenly snap out of REM sleep -- a deeper stage of sleep where you dream and your body repairs itself. During that sleep cycle your body is flooded with high levels of melatonin, the body's sleep hormone. Waking with a body packed full of a sleep aid causes disorientation and shaky sensory-motor performance that typically lasts about 30 minutes to an hour.
But if you're sleep deprived (and who isn't these days?), the grogginess can remain for two or more hours.
Sleep inertia can also happen when waking from a daytime snooze that went long, well past the 20 minute power nap that might refresh you.