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Glossary of Sleep Terminology I thru P

Sleep Terms

To help you better understand the terms you hear from sleep professionals, here are the definitions , I-P. (photo credit: BigStockPhoto.com)

In our previous post, we talked about common sleep terminology, A-I. This post continues on with that topic, covering sleep terminology you may hear while talking with a sleep professional. This article covers sleep terminology, I – P.


Insomnia – A sleep disorder or symptom of a sleep disorder that makes it difficult to fall asleep, stay asleep, or sleep at long as you want to.


Jet Lag – A condition commonly experienced by people when they travel across several time zones that can cause fatigue, insomnia, and other symptoms.


K Complex – This is a wave pattern seen on an EEG that is associated with stage 2 sleep. An EEG waveform pattern with a distinct shape; associated with N2 (stage 2) sleep.


Melatonin – This is a hormone that plays a key role in sleep.  It is secreted as the amount of light decreases as a signal to the body that the time for sleep is approaching.  It is believed to play a role in circadian rhythm management.


Microsleep – This is a very short period of sleep, generally lasting only a few seconds, that can occur when someone is overtired and trying to stay awake.


Multiple Sleep Latency Test (MSLT) – This is a sleep test performed in a sleep lab that consists of several 20 minute naps over the course of a day and is used to measure a person’s sleepiness.   It can be beneficial in diagnosing sleep disorders like narcolepsy.


Narcolepsy – This is a sleep disorder that causes sudden, uncontrollable bouts of sleep and excessive sleepiness.


Night Terror – This is a type of sleep disturbance that causes panic during sleep.  It is similar to a nightmare but differs in three key ways.  Night terrors occur during non-dreaming sleep which means they lack the visual imagery associated with nightmares, it is difficult to awaken someone during a night terror because of the sleep stage they are in, and most people do not remember night terrors after they wake up.


Nightmare – This is a type of sleep disturbance that occurs during REM sleep and is caused by dreams with frightening content.


Nocturnal – This describes someone or something that is active during the night rather than during the day.


Non-Rapid-Eye-Movement (NREM) Sleep – This includes the stages of sleep that are considered non-dreaming and that do not involve rapid eye movement.


Obstructive Sleep Apnea (OSA) – This is a sleep disorder that causes the person to stop breathing while they are asleep.  Those with the condition can experience several apneas, the period when breathing stops, in a single night, each of which can last from a few seconds to more than a minute.   The cessation of breathing is caused by an obstructed airway.


Parasomnias – These are sleep disorders or disturbances that involve involuntary behaviors that occur during sleep like sleep walking, sleep talking, and sleep eating.


Periodic Limb Movements Disorder (PLMD) – This is a sleep disorder that caused the person to experience random uncontrollable movements of their legs during sleep.  These movements generally occur every 20 to 40 seconds which can make it difficult to get quality sleep causing excessive daytime sleepiness.


Polysomnograph or Polysomnogram – This is what is commonly referred to as a sleep test and is performed in a sleep lab.  It involves recording several different things during sleep including brain waves, eye movements, muscle activity, breathing, heart rate, and other things.  This test is commonly used to diagnose sleep disorders.

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