Sleep inertia: Is there a worst time to wake up?

Sleep inertia, a brief period of inferior task performance and/or disorientation immediately after awakening from sleep could impact on military personnel required to work soon after awakening. The objective of this study was to determine whether severity of sleep inertia showed a circadian rhythm. Subjects underwent either 64-hr without sleep or 64-hr with a 20-min nap period every 6-hr. Sleep inertia was measured by performance scores of Baddeley's logical reasoning task. The effects of sleep inertia were additive to those of sleep deprivation. The severity of sleep inertia effects on performance were found not to show circadian variation, however, waking up from naps during the circadian temperature through was psychologically very difficult for the subjects. Sleep, Sleep Deprivation, Sleep Inertia, Cognitive Performance, Naps, Circadian Rhythms.