During sleep, a person moves through sleep stages one to four; the sleep cycle then reverses back through stages three and two to stage one (which, in the reverse order, is called emergent stage one). This cycle generally repeats several times during a night's sleep. As a sleeper passes on through stage two and back into stage one, the eyes begin to dart back and forth; REM (rapid eye movement) sleep and dreams occur. (REM sleep is also called paradoxical sleep because the brain activity, blood pressure, heart rate, etc., closely resemble those of waking consciousness.) Because neither dreams nor rapid eye movements occur in any of the other stages of sleep, those stages are called NREM (non‐rapid eye movement) sleep.
Sleep deprivation. When people go without sleep (sleep deprivation), especially if they have missed REM sleep, drastic changes in their behavior patterns occur. Sleep‐deprived people become tired, irritable, and lethargic.
Dreams. Analysis of dreams, which occur during REM sleep, is an important part of the psychoanalytic treatment for emotional problems. During the treatment process, patients report what they consciously remember about their dreams, the manifest content. In order to better understand their emotional problems, the analyst then has them use a process called free association to help determine the latent content (unconscious portion) of the dream.
Daydreams. Daydreams, as well as sleep, indicate an altered level of consciousness. They represent a shift in attention from ongoing events. People daydream most frequently at night just before they go to bed, but they may daydream any time, especially when engaged in a monotonous task. Daydreams have value because they provide relief from boredom through continuous and frequently changing stimulation; in addition, they permit the planning and imaginary trying out of solutions to problems.
Sleep disorders. The term sleep disorders refers to a variety of problems people have with the process of sleeping.
One of the most serious conditions is sleep apnea, a sometimes fatal disorder in which people momentarily stop breathing. At the least, this disruption of the breathing process causes the person to be sleepy the next day.
Narcolepsy, another serious sleep disorder, is a condition in which people suddenly fall asleep, even in the middle of another activity.
Insomnia, a common problem, is difficulty in falling asleep.
Somnambulism is sleepwalking.
Nightmares are bad dreams from which the sleeper may wake up aroused and frightened.