By Brandon R. Peters, M.D.
Quite simply, the experience of sleep paralysis sounds too crazy to be true. When it occurs, which it does with surprising frequency, the victim often questions his or her own sanity. It is not uncommon to ascribe the experiences to demonic possession, aliens, and any number of otherworldly phenomena. What exactly is sleep paralysis? Learn about this unusual experience and what science tells us about the likely cause.
Sleep paralysis can be experienced in an astonishing number of ways, but it tends to share a few common elements. First, it inevitably involves a transient inability to move or speak as you transition from sleep to wakefulness. You may feel absolutely frozen in place. Eye movements and breathing are always preserved, though some people experience a sense of breathlessness. This paralysis may be accompanied by vivid hallucinations. These hallucinations are often quite frightening, and may include seeing, hearing, smelling, or even feeling things that are not there.
Many of those afflicted with sleep paralysis report the perceived presence of a human figure at the bedside, often described as dark, like a ghost or a shadow. It tends to be just beyond the periphery of vision, and it is often menacing. This may be accompanied by a sensation of being touched, and some even describe feeling like they are being held down. Understandably, this experience in the middle of the night, as you come out of sleep, can be downright terrifying.
In fact, fear often accompanies the experience of sleep paralysis. Sleep paralysis can literally be a waking nightmare. Beyond the hallucination of a stranger's presence, some people have a sense that they may be experiencing a health crisis or even be dying. The occurrences are often recalled as being weird or strange, and though the episodes may last only minutes, the sense of helplessness may leave a lasting impression.
The Causes of Sleep Paralysis
Sleep paralysis is extremely common, if not widely discussed. Research studies suggest that between 20 and 60 percent of people have experienced it, depending on the population assessed. A smaller portion, perhaps one in 25 people, have had five or more episodes. It occurs throughout the world and goes by different names. For example, in Great Britain it is called the "old hag." What causes such an unusual and widespread condition?
There is no evidence that isolated sleep paralysis represents a serious medical or mental health problem. Just as dreams can be extraordinarily vivid and seem real as they are experienced, sleep paralysis can sometimes lead us into fanciful ways of explaining the occurrence. Was it a demon presence? Have the aliens finally arrived? Is my house haunted? Fortunately, it does not require a supernatural explanation. We understand the scientific rationale for the occurrence quite well.
Scientifically, sleep paralysis is understood to be related to the intrusion of rapid eye movement (REM) sleep elements into wakefulness. REM sleep is when we have our most vivid dreams. It occurs cyclically throughout the night, with these periods normally appearing every 90 to 120 minutes. During REM, the muscles of the body are actively paralyzed, so that the dreams are not inappropriately acted out. The muscles controlling the eyes and diaphragm remain active. The stuff of dreams floods our mind in REM, resulting in fantastical adventures if we are asleep -- or terrifying confusion if we are partially awake.
Indeed, this overlap accounts for the bizarre experiences reported as part of sleep paralysis. Sleep is not a switch that turns our brain on or off. In fact, mixed states of consciousness may occur. Parts of our brains may be both awake and asleep at the same time. The part that controls consciousness and memory may be turned off while the part that controls walking may be turned on, resulting in sleepwalking with no awareness or recollection. Similarly, we can be awake and looking around the room while the elements of REM sleep keep us unable to move and hallucinating wildly.
These mixed states are more likely to occur when the entire system is left unstable. Other sleep disorders may contribute, most particularly a rare disorder called narcolepsy. Sleep apnea or periodic limb movements of sleep may also fragment our sleep states and prolong the overlap as we transition. More commonly, irregular or inadequate sleep may make the states more tenuous and fluid. Anxiety, depression, shift work and alcohol use may also increase the incidence of sleep paralysis.
As sleep paralysis is most often infrequent and short-lived, it does not require any specific treatment. Many people are reassured by knowing it is nothing serious, that all their marbles are accounted for. If it becomes a more frequent visitor, you may wish to speak with a sleep specialist about some of the other possible causes of sleep fragmentation. For everyone else, take comfort knowing that these strange episodes have a clear explanation and are a widely shared experience.
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Brandon R. Peters, M.D., is the writer on sleep for About.com, a neurology-trained sleep medicine specialist in Novato, Calif., and consulting assistant professor at the Stanford Center for Sleep Sciences and Medicine. This Center is the birthplace of sleep medicine and includes research, clinical, and educational programs that have advanced the field and improved patient care for decades. To learn more, visit us at: sleep.stanford.edu.