Sleep paralysis

Sleep paralysis is a phenomenon in which a person either during falling asleep (hypnagogia) or awakening (hypnopompia), temporarily experiences an inability to move, speak, or react.

It is a transitional state between wakefulness and sleep, characterized by muscle atonia (muscle weakness). It is often accompanied by terrifying hallucinations (such as an intruder in the room) to which one is unable to react due to paralysis, and physical experiences (such as strong current running through the upper body).

One hypothesis is that it results from disrupted REM sleep, which normally induces complete muscle atonia to prevent sleepers from acting out their dreams. Sleep paralysis has been linked to disorders such as narcolepsy, migraines, anxiety disorders, and obstructive sleep apnea; however, it can also occur in isolation.

Classification

The two major classifications of sleep paralysis are isolated sleep paralysis (ISP) and the significantly rarer recurrent isolated sleep paralysis (RISP). ISP episodes are infrequent, and may occur only once in an individual's lifetime, while recurrent isolated sleep paralysis is a chronic condition, and can recur throughout a person's lifetime. RISP episodes can last for up to an hour or longer, and have a much higher occurrence of perceived out of body experiences, while ISP episodes are generally short (usually no longer than one minute) and are typically associated with the intruder and incubus visitations. With RISP the individual can also suffer back-to-back episodes of sleep paralysis in the same night, which is unlikely in individuals who suffer from ISP.

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See also

Sleep

Sleep is a naturally recurring state of mind characterized by altered consciousness, relatively inhibited sensory activity, inhibition of nearly all voluntary muscles, and reduced interactions with surroundings. It is distinguished from wakefulness by a decreased ability to react to stimuli, but is more easily reversed than the state of hibernation or of being comatose. Mammalian sleep occurs in repeating periods, in which the body alternates between two highly distinct modes known as non-REM and REM sleep. REM stands for "rapid eye movement" but involves many other aspects including virtual paralysis of the body.

During sleep, most systems in an animal are in an anabolic state, building up the immune, nervous, skeletal, and muscular systems. Sleep in non-human animals is observed in mammals, birds, reptiles, amphibians, and fish, and, in some form, in insects and even in simpler animals such as nematodes. The internal circadian clock promotes sleep daily at night in diurnal species (such as humans) and in the day in nocturnal organisms (such as rodents). However, sleep patterns vary widely among animals and among different individual humans. Industrialization and artificial light have substantially altered human sleep habits in the last 100 years.

Paralysis

Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage as well as motor. About 1 in 50 people have been diagnosed with some form of paralysis, transient or permanent. The word comes from the Greek παράλυσις, "disabling of the nerves", itself from παρά (para), "beside, by" and λύσις (lysis), "loosing" and that from λύω (luō), "to loose". A paralysis accompanied by involuntary tremors is usually called "palsy".

Causes

Paralysis is most often caused by damage in the nervous system, especially the spinal cord. Other major causes are stroke, trauma with nerve injury, poliomyelitis, cerebral palsy, peripheral neuropathy, Parkinson's disease, ALS, botulism, spina bifida, multiple sclerosis, and Guillain-Barré syndrome. Temporary paralysis occurs during REM sleep, and dysregulation of this system can lead to episodes of waking paralysis. Drugs that interfere with nerve function, such as curare, can also cause paralysis. There are many known causes for paralysis, and perhaps more yet to be discovered.