REM sleep behavior disorder (RBD) is a sleep disorder classified as a sleep disorder that involves abnormal behaviors during a stage of sleep called REM sleep. It was first described in 1986. The main and only characteristic of this disorder is the loss of the normal paralysis and relaxation that occurs to the skeletal muscles in a normal and necessary way during REM sleep, which leads to various behavioral complications during sleep ranging from small tremors in the limbs to complex full movements that a healthy person does not normally perform during this stage. Since dreams occur during this stage specifically, the loss of the normal inhibition of skeletal muscle movement may lead the affected person to physically act out their dreams without being aware of it; as a result, the person may make violent movements based on what he sees in his dreams, which may cause him to harm himself or his partner who sleeps next to him. As previously mentioned, the affected person acts out his dreams with body movements without being aware of it, and depending on the nature of the dreams he sees, the movements he makes may include kicking, punching, screaming, and even jumping out of bed. Although the person remembers his dreams after waking up, which match the movements he acted out, he is unable to remember any of these movements and does not realize that he made them. In the normal sleep cycle, the sleeping person goes through the REM sleep stage in several periods separated by a period ranging from an hour and a half to two hours each night, which means that the symptoms of the disorder may occur four times in one night. They occur most often in the early morning hours, as the REM sleep stage occurs during these hours more than others. In rare cases, these symptoms may occur once a week or once a month. Another symptom of this disorder is that the affected person may respond to and interact with other people without knowing it, and as a result of these symptoms, the person suffers from sleep deprivation. This disorder is likely to be the result of harmful interactions with some medications or abstinence from medication. Whatever the cause, it most often affects older adults and those with neurodegenerative disorders and diseases such as Parkinson's disease, multiple system atrophy, and Lewy body dementia. The disorder is classified by cause into two categories: idiopathic and episodic. This type occurs when the sleep structure is normal, but there is a marked increase in the density of REM sleep and the percentage of slow-wave sleep. As observed through familial genotypes, this category is strongly associated with the presence of a genetic factor. This category, which is more common than the first, is closely associated with neurodegenerative diseases, but it is not certain whether these diseases precede the occurrence of the disorder, occur simultaneously with it, or precede it. The strength of the relationship with these diseases is demonstrated by the fact that about 15% of Parkinson's patients also suffer from this disorder, as do 70% of patients with multiple system atrophy, and 85% of patients with Lewy body dementia. Other diseases documented to be related to this disorder include: Scheideregger syndrome, olivopontocerebellar atrophy, multiple sclerosis, cerebrovascular diseases, Tourette syndrome, and Guillain-Barré syndrome. Researchers have studied the relationship between functional behavior of the body and the appearance of symptoms specific to REM sleep behavior disorder, and the results have shown associations with dysfunction of the central nervous system and abnormal activity of the cerebral cortex during the REM sleep phase; which includes decreased beta waves in the occipital lobe and increased theta waves in the frontal and occipital lobes. Magnetic resonance imaging studies have indicated dysfunction in the frontal lobe and pons in patients with this disorder; as a result of decreased blood flow in these two parts of their brains compared to those without the disorder. Electromyography studies revealed an increase in the intensity of chin muscle tone, in addition to the presence of phase twitching in the limbs and prolonged hyperactivity. Another cause of this disorder is damage to the nerve impulses in the brainstem; those responsible for managing the phenomenon of rapid eye movement sleep. Due to the possibility of confusion between this disorder and other sleep parasomnias, it is necessary to perform basic sleep studies such as polysomnography in centers specialized in evaluating and distinguishing between sleep parasomnias in order to reach the correct diagnosis. One night of intensive monitoring of sleep, brain and muscle activity is sufficient to indicate the absence of paralysis that naturally occurs in the skeletal muscles during the REM sleep phase. It is also sufficient to exclude other causes of various sleep parasomnias. Due to the limited application of polysomnography currently, many attempts have been made to identify the disorder through clinical interviews and questionnaires. One of these attempts was made by Posthuma et al. when they demonstrated the feasibility of applying a single-question screening tool, which can be easily applied to the patient and his bed partner in general medical practice. This test includes the question "Have you ever reported or suspected that you make movements during your sleep that seem to act out your dreams?" If the person answers yes, this helps the doctor diagnose the condition as REM sleep behavior disorder; this is because this tool has a good sensitivity of 94% and a specificity of 87%. Other questionnaires that provide more detailed descriptions include the REM sleep behavior disorder screening questionnaire and the Hong Kong REM sleep behavior questionnaire. The disorder is treatable, and medications are prescribed based on the accompanying symptoms. One of the medications used is clonazepam, which is the most effective with a success rate of 90% when used in low doses. The way this drug works to restore muscle tonicity in REM sleep is not clear, but it is thought that it works by inhibiting muscle activity rather than directly restoring tonicity. For those with Parkinson's disease who also have the disorder, levodopa is a popular option, and pramipexole is also effective. Melatonin, a natural alternative, is also effective. Recent evidence has shown similar efficacy for melatonin and clonazepam when used as both drugs to control REM sleep behavior disorder, with patients who used melatonin experiencing fewer side effects than those who used clonazepam. Additionally, patients with neurodegenerative disorders such as Parkinson's disease have reported better outcomes when treated with melatonin. In addition to medication, it is wise to secure the sleeping environment and prepare it for attacks of the disorder by removing dangerous objects from the bedroom, placing pillows around the bed, or placing the mattress on the floor for additional protection against falls and injury. Patients are advised to follow a consistent sleep schedule, avoid sleep deprivation by getting enough sleep, and monitor their sleep schedule. Treatment also includes managing neurological symptoms and treating other sleep disorders. Anything else that might increase the negative effects of the disorder, such as alcohol and some medications, should also be avoided. The most comprehensive assessment to date estimates the prevalence of the disorder at 0.5% in people aged 15 to 100. The average age of onset is around 60. Studies suggest that the disorder is more common in males, with females accounting for only 10% of those affected. This is partly due to statistical bias; men’s movements during sleep are more likely to be violent than those of women, and are more likely to cause harm and damage, and are therefore more documented. In addition, the harm that a woman may suffer from the movements of her afflicted husband is more documented than harm to a man if the woman is the one suffering from the disorder. However, this does not negate the possibility that the difference is real due to genetic factors or male factors. There are many conditions that resemble REM sleep behavior disorder in that patients suffer from excessive sleep movement that may lead to violent behaviors. These disorders include sleepwalking and sleep terror disorder associated with other stages of sleep. They also include nocturnal seizures and obstructive sleep apnea, which can provoke complex behaviors during REM sleep. As a result of the similarity between these conditions, polysomnography plays an important role in diagnosing REM sleep behavior disorder. It is clear that this disorder shares many things with a group of different conditions and disorders such as narcolepsy. Both—REM sleep behavior disorder and narcolepsy—involve a disruption of the normal sleep cycle caused by a disruption in the sleep-control mechanisms. Reported cases of the disorder, such as stroke and axonal tumors, suggest that damage to the brainstem may lead to the disorder. The disorder is usually chronic, but it can be acute and come on suddenly if it is caused by medication or abstinence, especially alcohol abstinence. Medications that may exacerbate the symptoms of the disorder and should be avoided in patients with it include monoamine oxidase inhibitors, tricyclic antidepressants, selective serotonin reuptake inhibitors, and noradrenergic antagonists. The disorder has also been diagnosed in animals, particularly dogs.