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However, if sleep drunkenness occurs at least once a week, it’s time to see a doctor. This refers to excessive daytime sleep as well as constant difficulty getting up in the morning. This could also be related to an underlying health condition. After sleeping, your brain doesn’t just suddenly wake up — it has to first go through a natural process called sleep inertia. You experience grogginess and perhaps the initial difficulty in getting out of bed right away.

Though specific mechanisms regarding brain function remain to be fully described—e.g. memory, consciousness—the physiology of brain mapping suggests that all areas of the brain have a function and that they are used nearly all the time. “The fact that you can do that at these high speeds indicates to us that what vision does is find concepts. That’s what the brain is doing all day long — trying to understand what we’re looking at,” says Mary Potter, an MIT professor of brain and cognitive sciences and senior author of the study.