Sleep inertia is that groggy feeling you may feel when you first wake up. It can make it very difficult to function at your best. Sleep inertia impairs both cognitive and psychomotor skills.
Many factors are involved in the characteristics of sleep inertia. The duration of prior sleep can influence the severity of subsequent sleep inertia.
Although most studies have focused on sleep inertia after short naps, its effects can be shown after a normal 8 hour sleep period. A critical factors is the sleep stage prior to awakening
Awakening during a stage 3 or 4 sleep produces more sleep inertia than awakening in stage 1 or 2. Waking up during REM sleep is in between. Some people experience sleep inertia even after short naps.
When a person has been sleep deprived, sleep inertia can last longer, even after a full night’s sleep. When there has not been sleep deprivation, the sleep inertia rarely lasts more than 30 minutes.
For napping, keep naps less than 45 minutes it minimize affects of sleep inertia.