There is usually a genetic predisposition for these phenomena, and they tend to be inherited from parents and run in families. Most are triggered by sleep deprivation from other underlying pre-existing sleep disorders (especially sleep apnea and restless legs syndrome/periodic limb movement disorder), as well as from stress, medications, alcohol abuse, etc, although they can also arise with no identifiable trigger (known as idiopathic). It is important to note that the occurrences are completely involuntary, and do not imply any underlying psychological disorder, as often used to be assumed.
sleep-talking or somniloquy, common in children (and not uncommon in adults) and largely harmless. Sleep-talking may occur when the body does not move smoothly from one stage of non-REM sleep to another, resulting in transitory partial awakenings, or less commonly a partial “motor breakthrough” during REM sleep (so that dreams are to some extent “acted out” aloud). The talking can vary from gibberish or indistinct mumblings to shouting or even complex monologues and dialogues. Sleep-laughing is another variant.
sleep-walking or somnambulism, quite common among pre-teens (it is experienced by about 10%-15% of children) and less so among adults (around 4%). Sleepers rise from deep slow-wave sleep in the early part of the night to perform activities usually performed during full consciousness, such as talking, walking, cleaning, cooking, even driving, for periods lasting up to ten minutes, all without any conscious awareness of what they are doing. Episodes occur with no warning, and usually with absolutely no subsequent memory. The eyes are usually open, but they appear not to be focusing. Occasionally, incidental injuries may arise, but usually it is not dangerous, and treatment is not normally necessary. Contrary to common belief, it is generally quite safe to wake a sleepwalker, although often it may be easier just to lead them back to bed.
sleep-related eating disorder (SRED), also called sleep eating or night eating syndrome, a potentially dangerous variant or extension of sleep-walking in which the sufferer sleepwalks to the kitchen and eats and drinks at random, often including unhealthy fatty foods, raw foods, strange combinations of foods, or even toxic substances, cleaning fluids, etc. SRED is not driven by hunger or thirst, but is an involuntary activity, totally unrelated to normal eating needs and preferences. In severe cases, the practice can lead to obesity, diabetes, hypertension or other diet-related problems, and accidents may occur at any time from using knives and appliances, or ingesting poisonous products.
sleep-sex or sexsomnia, sexual acts, ranging from masturbation and sexual vocalizations to full intercourse and actual sexual assault, performed while still asleep, and usually not remembered afterwards. Like many parasomnias, sleep-sex may be triggered by sleep deprivation, alcohol or stress, and is often associated with sleep apnea.
night terrors, or sleep terrors or pavor nocturnus, intense, violent and inconsolable feelings of terror or dread experienced on waking from deep slow-wave sleep, mainly among young children (about 6%) and younger adults (about 2%). The events are often accompanied by screaming, thrashing around (sometimes with almost superhuman strength and speed), and are usually followed by a period of confusion and almost complete amnesia about the incident. Unlike nightmares, which occur during the main dream sequence of REM sleep and which usually involve complex dream scenarios, night terrors appear to be very brief, hair-trigger responses to very small stimuli (such as strange noises, for example) during non-REM sleep, and usually have no clear narrative, just a generalized feeling of dread. Medication is usually quite successful in controlling the occurrences, but resolution of the underlying sleep disorder and good sleep hygiene are better long-term solutions.
confusional arousals, also known by the descriptive phrase “sleep drunkenness”, a similar but less violent experience than night terrors, quite common in children, where a period of movement and crying gives way to a partial and confused awakening, marked by disorientation, mental dullness, slurred speech and slowed reactions. Confusional arousals may be brought on by ongoing sleep deprivation, but also by alcohol abuse, medications, stress or other sleep disorders.
exploding head syndrome or auditory sleep starts, the hallucinatory experience of a sudden loud noise, like an explosion, gunshot, cymbal clash or roar, sometimes accompanied by a flash of light, apparently from within the sleeper’s own head just as they are about to fall asleep, causing a sense of fear or anxiety.
teeth grinding or bruxism, a common complaint, often caused by stress or anxiety, where the compulsive grinding of teeth, mainly during the light stages of non-REM sleep, can cause sleep disruption as well as tooth damage and jaw pain.
REM sleep behaviour disorder (RBD), a relatively rare but dramatic phenomenon, where the muscle atonia (the protective mechanism that causes immobilization during REM sleep) is partially or completely absent. Sufferers, predominantly older males, may therefore try to physically act out their dreams, often suffering (or causing) physical injuries in the process. To make things worse, the dreams involved are usually even more vivid and intense than usual, often involving classic fight-or-flight scenarios. Curiously, RBD patients rarely complain of fatigue, and it seems that restorative slow-wave sleep tends to increase in compensation. The condition is now thought to be a kind of degenerative brain disease, and RBD sufferers often go on to later develop Parkinson’s disease or similar neurological diseases. Medication is usually able to control this potentially dangerous condition.
catathrenia or nocturnal groaning, breath-holding during REM sleep, followed by a long drawn-out groaning, wheezing or squeaking sound during exhalation. The groans can last from 2 to 20 seconds each, and usually occur in clusters or episodes of 2 to 60 minutes throughout the night. The groaner does not normally feel tired after sleep, which does not appear to have been unduly disrupted, and tends to have no memory of the groaning.
sleep paralysis (also known as recurrent isolated sleep paralysis), the inability to perform voluntary actions, either at sleep onset or upon awakening, as a result of disrupted REM sleep. It is caused by a dissociation of REM activity, where the normal muscle atonia or paralysis of REM sleep “leaks into” wakefulness, resulting in a complete temporary inability to speak, move or respond in any way, despite the feeling of being awake, lasting anywhere from thirty seconds to several minutes. It is usually accompanied by laboured breathing, a vague sense of dread, and often a feeling of being crushed or sat upon. A full-blown attack may include additional symptoms such as a tingling sensation, bright lights in the head, buzzing or ringing the ears, hypnagogic or hypnopompichallucinations of threatening figures, like a kind of waking nightmare, and sometimes a feeling of floating, similar to an out-of-body experience. Despite its dramatic nature, this is actually a relatively common condition, and some 25%-30% of the population might expect to experience an episode at some point.