Types of Dreams

Just as there are different types of dreamlike experiences, there are different
kinds of dreams. While there will be shortcomings in any effort toward classifying
dreams, some approximate distinctions can be made in regard to sleep
stage, affect (feelings and emotions), reality orientation, and dream origin.
When people fall asleep, brain activity changes throughout the night in
cycles of approximately ninety minutes. Research with the electroencephalograph
(which records electrical activity) has demonstrated a sequence of
four stages of sleep occurring in these cycles. The first two stages are called
D-sleep (desynchronized EEG), which constitutes essential psychological
rest�"consolidation of memories and processing of thoughts and emotions.

The other two stages, which constitute S-sleep (synchronized EEG), are necessary
for recuperation from the day’s physical activity�"physical rest. Ssleep
usually disappears during the second half of a night’s sleep. Dreaming
occurs in both S-sleep and D-sleep but is much more likely to occur in Dsleep.
A further distinction in the physiology of sleep is pertinent to the type of
dreaming activity likely to occur. During stage one sleep there are often accompanying
rapid eye movements (REM) that are not found in other stages
of sleep. Researchers often distinguish between REM sleep, where these ocular
movements occur, and non-REM (NREM) sleep, in which there is an
absence of these eye movements. When people are aroused from REM
sleep, they report dreams a majority of the time�"roughly 80 percent�"as
opposed to a minority of the time�"perhaps 20 percent�"with NREM sleep.
Furthermore, REM dreams tend to have more emotion, greater vividness,
more of a plot, a greater fantastical quality, and episodes that are more likely
to be recalled and with greater clarity.

The prevalence of affect in dreams is linked with people’s styles of daydreaming.
Those whose daydreams are of a positive, uplifting quality tend to
experience the greatest amount of pleasant emotionality in their dreams.
People whose daydreams reflect a lot of anxiety, guilt, and negative themes
experience more unpleasant dreams. While most dreams are generally unemotional
in content, when there are affective overtones, negative emotions
predominate about two-thirds of the time. Unpleasant dreams can be categorized
into three types. Common nightmares occur in REM sleep and are
caused by many factors, such as unpleasant circumstances in life, daily stresses, or traumatic experiences. Common themes are being chased, falling,
or reliving an aversive event. Night terrors are most likely to occur in
stage four sleep and are characterized by sudden wakening, terror-stricken
reactions, and disorientation that can last several minutes. Night terrors
are rarely recollected. An extreme life-threatening event can lead to posttraumatic
stress disorder (PTSD). Recurring PTSD nightmares, unlike other
nightmares and night terrors, are repetitive nightmares in which the sufferer
continues to relive the traumatic event. Furthermore, PTSD nightmares
can occur in any stage of sleep.