Sleep inertia is defined as the groggy, disoriented feeling that comes with waking up. Sleep inertia is one of the main reasons people reach for that first cup of coffee.
While some people may feel disoriented only a few minutes after waking up, others suffer for as much as two hours.
Sleep inertia has been identified by the scientists and they conducted a research to see how it influences cognitive abilities. They found that many people are as mentally impaired when they wake up after a full night's sleep as if they were drunk
Volunteers in the study scored much worse on a series of tests immediately after waking than when they had gone without sleep for 24 hours. When they stayed up for 24 hours, they scored about 80 % as high as they would normally do while those who had a full night sleep scored only 65% of their average performance.
Previous researches on sleep deprivation found that not sleeping for 24 hours leaves people as mentally impaired as if they had a blood alcohol level of .08 per cent. The effects of sleep inertia may be as bad as or worse than being legally drunk.
Biological basis for early-morning grogginess has been found. People's brains were scanned after they had woken up. It was found that prefrontal cortex, which is believed to be responsible for problem solving and complex thought, takes longer to become active. It seems that blood flow increases to other areas of the brain first.
Scientists advise not to make important decisions before the mental fog lifts.