sleeping man Posted August 25, 2009.

I browsed a couple of books on chronobiology, a field of science that studies biological rhythms in humans, animals, and plants. I wanted to learn more about the stages of sleep and about the disruptions to those stages such as night terrors and sleep paralysis.
Explanations for the latter two have made their way into ghostly folklore across cultures.

Night terrors occur in the deep stage of sleep before the stage of dreaming or rapid-eye movement (REM). Like nightmares that occur in REM, night terrors are unusual states of arousal that disrupt the sleep stage they occur in.

Sleep paralysis occurs during the transition stage from rapid-eye movement (REM) to wakefulness. Sometimes your consciousness awakes before the rest of your body has come out of paralysis, a temporary form of paralysis that prevents you from moving and acting out your dreams, e.g., "I'm flying! I'm flying!"

Supernatural explanations for sleep paralysis come from the sensation of restraint or feeling like something is sitting on one's chest, call it a demon, witch, or ghost.

The creepiest thing I read though is how a person could have their eyes open while their brain is asleep and they could still be capable of minimal performance, like some L.A. freeway drivers on auto-pilot.

As for the question, How much sleep do you really need?, the answer depends, though it appears that 7 to 7.9 hours of sleep nightly is optimal and the threshold is 4.5 to 5 hours of sleep, less than that and you're fighting sleep during the day. Remind you of any coworkers on Mondays?
sun CIRCADIAN (DAILY) RHYTHMS
(24-hour solar day cycle, free-running 25-hour cycle)
moon
Stage Brain
Waves*
Description Behaviors of Interest
Alert Beta Body temperature rises to highest point about midday; marks high point of alertness.

90- to 110-minute brain activity cycles, from alertness to listlessness.
Relaxed Alpha Trance state of regular TV watchers.
*Brain waves are recorded using an electroencephalograph (EEG).
STAGES OF SLEEP
Stage Brain
Waves
Description Behaviors of Interest
Non-rapid Eye Movement (NREM)
1
(5-10 min.)
Theta Transitioning to sleep Night-shift paralysis: Reduced performance (auto-pilot) and dampened mobility.
Hypnagogic hallucinations
2 Theta Light sleep Person will respond to noise. When awoken, they may say they weren't sleeping.
3 to 4 Delta Deep stages of sleep

Body temperature drops to lowest point between 2:00 and 5:00 a.m.; marks low point of alertness.
Sleep talking (somniloquy)
Sleepwalking (somnambulism)
Bedwetting (sleep enuresis)
Night terrors (or sleep terrors): Physiological arousal that disrupts Stages 3-4 sleep. Extreme fear with screaming or shouting, but the person is half-asleep and may remember very little afterward.
Sleep apnea: Person ceases to breathe for up to 10 seconds, then snorts and starts breathing again.
Rapid-eye Movement (REM)
5
(20-25% of
total sleep)
Beta
(same as when
you are awake)
Large voluntary muscles, such as arms and legs, are in state of temporary paralysis, but brain is very active.

90- to 110-minute brain activity cycles, from Stages 1-2 to Stage 5, 4-6 times a night, with time in REM gradually becoming greater than time in Stages 3-4.

Narcoleptics, who fall asleep at unexpected times, skip NREM stages and go straight to REM from wakefulness.

Alcohol reduces REM.
Dreaming (what we do for 10% of our lives)
Dream interpretation: What do those symbols personally mean?
Dream telepathy: The chance of some predictions coming true can be explained by probability theory.
Nightmares: Physiological arousal that disrupts REM sleep.
Waking up Theta Transitioning to wakefulness Sleep paralysis: Consciousness returns before muscles come out of temporary paralysis. Best advice is to not fight it and to relax. Bodily control will return faster that way.
Hypnopompic hallucinations
More Info
"Brain Basics: Understanding Sleep," National Institute of Neurological Disorders and Stroke.
SleepEducation.com, American Academy of Sleep Medicine. This site has a complete list of sleep disorders.

Recommended Books
Wide Awake At 3:00 A.M.: By Choice or by Chance? by Richard M. Coleman. New York: W.H. Freeman and Co. 1986.