context: Parasomnias are disruptive sleep disorders that can occur during arousals from REM sleep or partial arousals from non- REM sleep. Parasomnias include nightmares, night terrors, sleepwalking, confusional arousals, and many others. Nightmares are vivid nighttime events that can cause feelings of fear, terror, and/or anxiety. Usually, the person having a nightmare is abruptly awakened from REM sleep and is able to describe detailed dream content. Returning to sleep is usually difficult. Nightmares can be caused by many factors, including illness, anxiety, the loss of a loved one, or negative reactions to a medication. Call your doctor if nightmares occur more than once a week or if nightmares prevent you from getting a good night's sleep for a prolonged period of time. A person experiencing a night terror abruptly awakes from sleep in a terrified state, but is confused and unable to communicate. They do not respond to voices and are difficult to fully awaken. Night terrors last about 15 minutes, after which time the person usually lies down and appears to fall back asleep. People who have night terrors (sometimes called sleep terrors) usually don't remember the events the next morning. Night terrors are similar to nightmares, but usually occur during deep sleep. People experiencing sleep terrors may pose dangers to themselves or others because of limb movements. Night terrors are fairly common in children, mostly between ages 3 and 8. Children with sleep terrors will often also talk in their sleep or sleepwalk. This sleep disorder, which may run in families, also can occur in adults. Strong emotional tension and/or the use of alcohol can increase the incidence of night terrors among adults. Sleepwalking occurs when a person appears to be awake and moving around, but is actually asleep. He or she has no memory of the episode. Sleepwalking most often occurs during deep non- REM sleep (stages 3 and 4 sleep) early in the night and it can occur during REM sleep in the early morning. This disorder is most commonly seen in children between ages 5 and 12; however, sleepwalking can occur among younger children, adults, and seniors. Sleepwalking appears to run in families. Contrary to what many people believe, it is not dangerous to wake a person who is sleepwalking. The sleepwalker simply may be confused or disoriented for a short time upon awakening. Although waking a sleepwalker is not dangerous, sleepwalking itself can be dangerous, because the person is unaware of his or her surroundings and can bump into objects or fall down. In most children, it tends to stop as they enter the teen years. Confusional arousals usually occur when a person is awakened from a deep sleep during the first part of the night. This disorder, which also is known as excessive sleep inertia or sleep drunkenness, involves an exaggerated slowness upon awakening. People experiencing confusional arousals react slowly to commands and may have trouble understanding questions that they are asked. In addition, people with confusional arousal often have problems with short-term memory; they have no memory of the arousal the following day. Rhythmic movement disorder occurs mostly in children under age 1. A child may lie flat, lift the head or upper body, and then forcefully hit his or her head on the pillow. Rhythmic movement disorder, which also has been called "head banging," also can involve movements such as rocking on hands and knees. The disorder usually occurs just before a person falls asleep. Sleep talking is a sleep-wake transition disorder. Although it usually is harmless, sleep talking can be disturbing to sleep partners or family members who witness it. Talk that occurs during sleep can be brief and involve simple sounds, or it can involve long speeches by the sleeper. A person who talks during sleep typically has no recollection of the actions. Sleep talking can be caused by external factors, including fever, emotional stress, or other sleep disorders. Nocturnal leg cramps are sudden, involuntary contractions most commonly of the calf muscles during the night or periods of rest. The cramping sensation may last from a few seconds to 10 minutes, but the pain from the cramps may linger for a longer period. Nocturnal leg camps tend to be found in middle-aged or older populations, but people of any age can have them. Nocturnal leg cramps differ from restless legs syndrome, because the latter usually does not involve cramping or pain. The cause of nocturnal leg cramps is not known. Some cases of the disorder can occur without a triggering event, while other causes of leg cramps may be linked to prolonged sitting, dehydration, an overexertion of the muscles, or structural disorders (such as flat feet). Muscle-stretching, exercise, and adequate water intake may help prevent leg cramps. People with sleep paralysis are not able to move their body or limbs either when falling asleep or waking up. Brief episodes of partial or complete skeletal muscle paralysis can occur during sleep paralysis. Sleep paralysis can run in families, but the cause of sleep paralysis is not known. This disorder is not harmful, but people experiencing sleep paralysis often are fearful, because they do not know what is happening. An episode of sleep paralysis often is terminated by sound or touch. Within minutes, the person with sleep paralysis is able to move again. It may occur only once in your lifetime or can be a recurring phenomenon. This disorder occurs among men who are unable to sustain a penile erection during sleep that would be sufficiently rigid enough to engage in sexual intercourse. Men usually experience erections as a part of REM sleep, and impaired sleep-related erections may indicate erectile dysfunction. Erections are a normal component of REM sleep for men. In rare cases, however, erections become painful and cause a man to wake up. The treatment of sleep-related painful erections may involve drugs that suppress REM sleep (some antidepressants, for example). A cardiac arrhythmia -- the medical term for an irregular heart rhythm -- is a change from the normal rate or control of the heart's contractions. People who have coronary artery disease and whose blood oxygen is lowered by sleep-disordered breathing may be at risk for arrhythmias, which take place during REM sleep. Continuous positive airway pressure ( CPAP) treatment may reduce this risk. People with rapid eye movement ( REM) sleep behavior disorder act out dramatic and/or violent dreams during REM sleep. REM sleep usually involves a state of sleep paralysis (atonia), but people with this condition move the body or limbs while dreaming. Usually, RBD occurs in men aged 50 and older, but the disorder also can occur in women and in younger people. It differs from sleepwalking and sleep terrors, in that the sleeper can be easily awakened and can recall vivid details of the dream. In the diagnosis and treatment of RBD, potentially serious neurological disorders must be ruled out. Polysomnography (sleep tests) and drug treatments also can be involved in the diagnosis and treatment of this disorder. Sleep bruxism -- or teeth grinding -- involves the involuntary, unconscious, excessive grinding or clenching of teeth during sleep. It may occur along with other sleep disorders. Sleep bruxism may lead to problems, including abnormal wear of the teeth and jaw muscle discomfort. The severity of bruxism can range from mild to severe enough to cause dental injury. In some cases, grinding can be prevented with the use of a mouth guard. The mouth guard, supplied by a dentist, can fit over the teeth to prevent them from grinding against each other. In this condition, the affected person is unable to maintain urinary control when asleep. There are two kinds of enuresis -- primary and secondary. In primary enuresis, a person has been unable to have urinary control from infancy onward. Primary bedwetting appears to run in families. Children are more likely to have it if their parents or siblings had it as children. In secondary enuresis, a person has a relapse after previously having been able to have urinary control. Enuresis can be caused by medical conditions (for example, diabetes, urinary tract infections, and sleep apnea) or by psychiatric disorders. Some treatments for bedwetting include behavior modification, alarm devices, and medications. This disorder is sometimes marked by seizure-like episodes during non- REM sleep. Most evidence points to NPD being a form of epilepsy. Episodes of NPD typically recur several times per night.