Sleep is a reversible behavioral state of perceptual disengagement from the environment and unresponsiveness to the environment, with total or partial unconsciousness.
Dreams are A collection of thoughts, emotions, and false sensory stimuli which occur in the mind during sleep. Most normal dreams last 5-20 minutes.
Sleep Stages:
N1 (alpha waves turn to theta waves), hypnic jerks 2-5% of sleep
N2 (sleep spindles, k complexes) 45-55% of sleep
N3 (delta) aka SWS sleep, formerly stages 3 and 4. SWS Dominates the first third of the night, but only 13-23% total.
Your muscles are not paralyzed in NREM sleep and NREM takes up a total of 75-80% of your sleep. Dreaming in NREM is rare.
REM 20-25% of sleep, usually 4-6 episodes, short at the beginning of the night, get longer as the night goes on. There are no brainwave patterns which dominate REM sleep. REM is characterized by atonia--loss of muscle tone, in other words paralysis, not to be confused with an episode of sleep paralysis.
One sleep cycle including all stages is about 90 minutes. It usually happens in the order of N1, N2, N3, N2, and REM.
Hallucination is a false perception characterized by a distortion of real sensory stimuli.
Hypnogagic hallucinations occur as we fall asleep.
Hypnopompic hallucinations occur as we're waking up.
HH can be any false sensation--most commonly sights and sounds, but also touches, tastes, and smells.
Sleep paralysis is an episode in which a person is usually transitioning from wake to sleep or sleep to wake and they find that they cannot move. SP is commonly characterized by hallucinations, vibrations, loud ringing or roaring noises in the ears, pressure on the chest or choking sensations, and often fear if impending doom or terror if the person is has no prior knowledge or experience of SP.
Physiologically speaking SP is caused by atonia of the voluntary muscles due to the REM cycle. It is still unknown exactly how the body triggers this and has been the subject of much study. So basically, an episode of SP occurs because you are either entering or exiting REM sleep and you have become conscious during this transition.
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