ABSTRACT
Sleep is a state of reduced awareness and responsiveness to internal and external stimuli. The reduced awareness is selective and it is stimuli of significance to the individual that are most likely to cause arousal from sleep.1 Sleep is also a transient phase that alternates with wakefulness and from which, unlike coma, the subject can be aroused quickly. The transition between wakefulness and sleep, however, may last for several minutes, and it may be impossible to determine the exact moment of falling asleep. In these transitional states, some aspects of both sleep and wakefulness coexist. Similarly, physical incoordination, sometimes with confusion, is common after waking from sleep (sleep inertia), probably due to delayed activation of the prefrontal cortex at the transition from sleep to wakefulness. The hallucinations associated with delirium such as delirium tremens probably represent partial rapid eye movement (REM) sleep intrusion into wakefulness. Sleep paralysis is also intrusion of the skeletal muscle relaxation of REM sleep into wakefulness.
