The body during non-REM sleep. We have a uniform heart rate
and breathing. The eyes move slowly, in contrast to the rapid eye
movements of REM. The body is not experiencing "sleep paralysis,"
but neither is it receiving instructions for movement.
The body during dreams. It experiences an increase in heart
rate, blood pressure, gastric acid (in people who have ulcers),
body temperature, metabolic rate, blood flow in the brain, and
glucose consumption. Certain hormones are released, but others are
suppressed. The heart also becomes more vigorous; this might be
one reason for the heart attacks which some people experience
during sleep. Our respiration rate varies according to the content
of the dream; if we dream that we are running, we breathe rapidly.
(During lucid dreams, our heart rate and oxygen consumption are
even higher than they are during non-lucids.) Our large muscles
become very relaxed and, in a sense, paralyzed (thus, "sleep
paralysis") -- probably so that those muscles cannot "act out" any
dreams which occur; however, muscles might twitch in the face and
fingers. The sexual organs are stimulated (particularly if the
dream has sexual content, or if the dreamer during wakefulness has
been sexually aroused or deprived); a man experiences an erection
(partial or full), and a woman's vagina becomes moist. The body is
more physiologically active during later REM periods than it is
during the first period.
The eye movements. During a study of sleep-time EEG readings
in the 1950s, Eugene Aserinksy and Dr. Nathaniel Kleitman
"discovered" rapid-eye movements in infants; their first series of
subsequent experiments were based on the assumption that REM
occurred only in infants, and only later did they find that adults
also exhibit REM. The rapid-eye movements during REM occur
probably because we look at moving objects in our dreams. In
lucid-dream experiments, when people moved the eyes of their
dream-body in a left-right pattern, their physical eyes moved
accordingly. Eye movements are measured in a sleep lab by an
What is sleep paralysis? It is a natural condition which
occurs when we are in REM sleep; we might become aware of it when
we are falling asleep into REM or waking up from REM. In this
state, we are unable to move or speak. This is called "the
cataleptic state" in Oliver Fox's book, Astral
Why does sleep paralysis happen? During REM sleep, a dream
seems real because the brain is issuing commands to the muscles to
enact the action which is depicted in the dream; from the
perspective of those parts of the brain, the dream scenario is
happening physically. Obviously we would be endangered if we
walked and ran in our sleep (with eyes closed and no sensory input
from the physical world). To protect us, the brain paralyzes most
muscles so that they cannot respond to the commands; this
condition is described medically as a "profound loss of muscle
tone." The paralysis is accomplished by "neural inhibitors" in the
bloodstream; in experiments where these inhibitors were blocked in
cats (chemically or by surgically removing the parts of the brain
which inhibit motor activity during dreams), the animals
dramatized their REM sleep with vigorous movement. We might
experience sleep paralysis consciously when we wakefully enter the
REM state -- or when we awaken directly from REM (and, for some
reason, the endocrine system continues to release the neural
inhibitors which sustain the paralysis).
Sleep paralysis is not total. The exempt muscles include those
of the lungs and heart -- and the eyes, as in "rapid eye
movement." The heart and lungs are obviously needed for the
maintenance of life, but we can only wonder why the eyes are also
excluded. Other parts of the body are able to exhibit some
movement. Paralysis is most thorough in the large muscles (and the
voice muscles) which would dramatize our dream (but we have all
seen dogs twitching their legs during apparent dreams). In
laboratory tests, dreamers were awakened to describe their dream
actions; the muscles which would correspond to those actions had
been registering slight movements and increases in muscle tension
and electrical activity. During tests on lucid dreamers, the
paralysis was more acute, but the sleeping subjects were able to
consciously create physical-body twitches in their hands,
forearms, and feet (with an intensity corresponding to the
dream-body's experience). The lucid dreamers could also control
their breathing -- "holding" it or breathing rapidly.
Some people don't experience sleep paralysis. This rare
condition, REM Sleep Behavior Disorder, prevents sleep paralysis,
so the victims act out their dreams with some or all of their
muscle facility. Imagine the danger and destruction which would
occur if we portrayed some of our dreams and nightmares; one man
who has this condition dreamed that he was attacked by a wild
animal, and when he tried to break its neck, he was awakened by
the screams of his wife whom he had supposed to be the beast.
Sleep paralysis is harmless but it might be frightening. When
I first experienced sleep paralysis, I had never heard of it; I
awoke but could not move, and I was overwhelmed by terror and
confusion. Now I know that sleep paralysis is a normal component
of REM sleep; in that instance, I went back to sleep, but the
immobilization would have dissipated soon after this awakening
anyway. When sleep paralysis occurs, all that we can do is wait
for the condition to wear off, while gently trying to move our
facial muscles and other muscles. However, sleep paralysis might
be fatal to infants; some researchers have speculated that SIDS
(Sudden Infant Death Syndrome) occurs when the neural inhibitors
are released in excessive amounts, paralyzing not only the muscles
which need to be constrained but also the heart and lungs.
Certain effects might accompany wakeful sleep paralysis.
During my first incident of sleep paralysis, another phenomenon
added to the horror: I saw the image of a sinister-looking
"spirit" sitting next to me, and I concluded that it must be
causing the paralysis as part of an "attack." (I apparently
misunderstood the paralysis, but I believe that the spirit
presence was real.) By the time I had my second experience of
sleep paralysis, I had read about it, but I was too groggy to
identify my condition as such; I distinctly heard the sounds of
two or three people walking around in my bedroom, and then I felt
them running their hands across my body -- and I wanted to jump up
and defend myself, but I was could not move, and I thought that
the paralysis was due to terror. During sleep paralysis, many
people say that they are assaulted by images which resemble
people, monsters, succubi and incubi (which are explained in the
chapter on nightmares), or a general fiendish presence. They might
also experience hallucinations, sounds (buzzing, hissing,
roaring), and bodily sensations (vibrations, electricity, a sense
of being touched, difficulty in breathing, or a weight on the
chest). Some people feel that they are leaving their body; this
and the other symptoms do parallel those of the out-of-body (OBE)
Sleepwalking. Sleepwalking -- or
somnambulism -- is one of our most unusual sleep activities.
The characteristics of sleepwalking. Sleepwalkers have certain
attributes in common.
The families. Sleepwalking is a typical, normal activity of
young children; most people outgrow it (but the behavior is
often passed to their children).
Abilities. Sleepwalking children tend to move awkwardly and
can perform only simple tasks. Adults have achieved complex
actions, such as driving a car.
Behaviors. Sleepwalkers often engage in repetitive
movements; e.g., opening and closing a door incessantly. They
might pursue a forbidden venture, such as eating food which is
not permitted by their diet.
The wakeful precursors. Sleepwalking is most likely to
occur when the wakeful activities have precipitated an
unusually deep "stage 4" during the first cycle of the sleep
period. That condition might have been caused by exhaustion
(from strenuous wakefulness or from previous lack of sleep).
The length of time. Sleepwalking usually ends within 15
The motivation. Sleepwalkers are generally prompted by fear
or concern; they get out of bed to resolve an imagined problem.
They are not responding to a REM dream.
Sleepwalking and REM. Sleepwalking does not occur during REM
sleep, when "sleep paralysis" would prevent movement. It usually
happens approximately one hour after the start of sleep, when we
are in stage 4 of the first cycle. When sleepwalking occurs, this
stage 4 period lasts for an extended period of time, and it is
occasionally interrupted by brief arousals.
The dangers of sleepwalking. Perception is limited during this
state, so sleepwalkers have fallen from balconies and staircases,
or walked into furniture or traffic, or suffered injuries from
sharp objects (or from the windows which they break). The
sleepwalker's environment should be a safe one -- with no
dangerous items, and a door which cannot be opened by the sleeper.
Sleeptalking. This related phenomenon generally occurs during
non-REM sleep; at that time, the utterances tend to be illogical
and unintelligible. However, sleeptalking can also occur during
REM sleep, because sleep paralysis does not affect breathing, and
the vocal apparatus is able to move enough to simulate speech.
During REM, the discourse is more likely to make sense.