Often times the subject arrives at the testing site exhibiting cooperative behavior and initiative, behaviors which extend into the second day, after one night of sleep deprivation.  The second night of sleep deprivation, the subjects will often need assistance in staying awake.  The hours between 3 and 5 am are, for many reasons, the “worst” parts of the sleep deprivation.  This is a low point in the human circadian rhythm, during which many physiological event occur, like a drop in the daily temperature cycle.  When lengthy performance tests are administered during this night, the subject will often fall asleep, but deny doing so when the researcher arouses them.

By the third day, subjects are no longer exhibiting behavior that suggests cheerfulness. An increase in listless social conversation may begin due to the fact that boring conversation still provides enough stimulation to remain awake yet not exert too much effort or attention. Mistakes in speech occur and subjects may begin to trail off during conversation.  The subjects are serious, tense, and unenthusiastic about being assigned performance tasks.  At this point, tests determining reaction time indicate that subjects' reaction time varies from normal to three times that length.  As more time passes, reaction times get progressively more uneven.  Decreases in sensory acuity are often recorded as well as the ability to memorize.  Subjects become increasingly indifferent and apathetic and, when disturbed, respond with irritability.  Rapid mood changes begin to occur and the urge to sleep increases to a level such that the third sleepless night is only accomplished with the help of researcher prodding.  The only successful techniques used to maintain arousal at this point involve some form of physical movement, like exercising.

    Subjects develop strong preference to types of performance tests once sleep deprivation has begun.  Tasks that involve sentry duties or surveillance, or those with a low participation requirement are eschewed while performance tests that involve high incentive tasks are preferred.  Subjects prefer to participate in these tests in groups rather than individually.  Self-paced tasks are also preferred over timed tasks.  The error percentage in timed tasks is much greater, indicating a more chances at reward, rather it is payment of some kind or just the knowledge that the task was completed correctly).  Some researchers have found that an extreme amount of effort may be able to compensate for, and mask, some effects of sleep deprivation because a few studies have produced results suggesting that steadiness, aiming accuracy, muscle strength, ability to name letters, and mental arithmetic remain normal during total sleep deprivation.

    After the early morning hours of the third night the urge to sleep weakens and microsleep becomes observable.  After a period of microsleep intervals, subjects often report feeling as if they are functioning at full awareness.  However, performance decrements have been reported in color and opposite-naming, body and hand steadiness, mental arithmetic, reading, and visual and auditory reaction time.  At this point, researchers begin to observe indication of perceptual disturbances.  Borbely suggests that at this point, the line between waking and sleeping is blurred such that the types of hallucinations that occur during sleep invade the waking state. Evidence that the subject experience illusion, incorrect perception of existing objects, and hallucinations, perception of non-existent objects, is observed at this point.  Participants report that the surfaces of objects begin to waver or that cobwebs appear on the floor.  Often times patients will see faces come and go or experience auditory illusions, like that the sound of running water is actually people talking.  Subjects may also remark that they are wearing a hat, but are not, due to the sensation of a ring pressure around the forehead, an occurrence sometimes called the “hat phenomenon.”

    After fourth day of total sleep deprivation, researchers observe delusions in addition to illusion and hallucinations.  Participants often show signs of paranoia and suspicion, indicating their belief that events and conversations are going on behind their backs that they are not being told about.  They may experience heightened suggestibility, meaning that they are more likely to believe things that they would be less credulous about in a non-sleep deprived state.  Symptoms of depersonalization may manifest themselves after the fourth day of deprivation.  In this phenomenon, subjects begin to lose clear sense of their own identities.  The inability to relate to the normal world also occurs.  As is expected, performance decrements are observed to progressively increase in severity with increased sleep deprivation.  For example, performance after 72 hours of wakefulness was considerably worse than after 50 hours of wakefulness.

    Researchers suggest that a single sleep period following most lengthy (3-7 day) studies of total sleep deprivation is adequate for restoration of performance deficits and psychological disturbances.