have a good sleep efficiency (>90%). They may have difficulty waking up in the morning,
sometimes appearing confused, co mbative, or ataxic. This pr olonged impairment of alert-
ness at the sleep-wake transition  is often referred to as sleep inertia  (i.e., sleep drunkenness).
It can also occur upon awaken ing from a daytime nap. During that period, the individual
appears awake, but there is a decline in moto r dexterity, behavior may be very inappro-
priate, and memory deficits, di sorientation in time and spac e, and feelings of grogginess
may occur. This period may last some minutes to hours. 
The persistent need for sleep can lead to auto matic behavior (usually of a very routine,
low-complexity type) that the individual carrie s out with little or no subsequent recall. For
example, individuals may find themselves having driven several miles from where they
thought they were, unaware of the “automatic”  driving they did in the preceding minutes.
For some individuals with hypersomnolence disorder, the major sleep episode (for most
individuals, nocturnal sleep) has a duration of 9 hours or more. However, the sleep is often
nonrestorative and is followed by difficulty awakening in the morning. For other individ-
uals with hypersomnolence disorder, the majo r sleep episode is of normal nocturnal sleep
duration (6–9 hours). In these cases, the excessive sleepiness is characterized by several un-
intentional daytime naps. These daytime naps tend to be relatively long (often lasting 1 hour
or more), are experienced as no nrestorative (i.e., unrefreshing),  and do not lead to improved
alertness. Individuals with hypersomnolence have daytime naps near ly everyday regard-