Several factors contribute to triggering sleepwalking episodes in those that are prone to the disorder, but the actual physiological cause of sleepwalking has not yet been fully established. Experts have long noted that sleepwalking tends to run in families and likely has a genetic component. A new study has established that the cause is likely a mutated gene that is passed down from parent to offspring. Those that have the mutated gene tend to suffer from the sleep disorder while those without it do not. Moreover, there is a fifty percent chance that a parent with the gene will pass it on to an offspring. A child who has a first-degree relative that sleepwalks is ten times more likely to suffer from the disorder. 
Common Triggers of Sleep Walking in Adults
For adults that are prone to sleepwalking several factors can trigger an episode including environmental factors, underlying medical conditions, and psychological disorders.
Environmental Triggers of Sleepwalking
Sleep deprivation has been identified as a common trigger to sleepwalking episodes. Sleepwalking episodes occur during the slow-wave stages of sleep and sleep deprived individuals seem to have difficulty passing through these stages increasing the incidence of sleepwalking. 
Other such environmental factors are also commonly cited as increasing the risk of a sleepwalking episode such as fatigue, irregular sleep schedules, stress, and a full bladder.
Studies have indicated that several psychological disorders contribute to the incidence of sleepwalking. Those with alcohol dependence or abuse and those that suffer from obsessive-compulsive disorders are more likely to encounter episodes of sleepwalking. One study indicated that those with depression are 3.5 times more likely to sleepwalk than those that do not.  Other conditions include posttraumatic stress disorder and dissociative states.
Medications that Contribute to Sleepwalking
There are certain classes of medication that can induce sleepwalking episodes that include sedatives, neuroleptics, stimulants, and antihistamines.  Such drugs include chloral hydrate, desipramine hydrochloride, lithium carbonate, prolixin, perphenazine, and thioridazine hydrochloride.  One study found that those taking SSRI antidepressants are three times more likely to sleepwalk. 
Certain medical conditions can trigger sleepwalking episodes and include arrhythmias, fever, gastroesophageal reflux, nighttime asthma, nighttime seizures, and obstructive sleep apnea. 
If your sleepwalking episodes are brief and infrequent, no medical treatment is usually required. However, if these episodes occur several times a week you should consult your doctor for a physical evaluation. In many cases of adult sleepwalking, the frequency and severity of nighttime episodes greatly diminishes once the cause of the condition is discovered and treated. Your doctor may also prescribe prescription medications that may help you sleep more deeply and avoid sleepwalking episodes or decrease their frequency. To avoid injury, be sure to lock all windows in your home and clear all obstacles that could cause injury if sleepwalking occurs.
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Sleep Disorders: Sleepwalking Basics
THE INTERNATIONAL CLASSIFICATION OF SLEEP DISORDERS, REVISED
Diagnostic and Coding Manual
Glossary of Terms
Arrhythmias: An arrhythmia is a disorder of the heart rate (pulse) or heart rhythm, such as beating too fast (tachycardia), too slow (bradycardia), or irregularly.
US National Library of Medicine
Dissociative State: In psychology and psychiatry, a perceived detachment of the mind from the emotional state or even from the body. Dissociation is characterized by a sense of the world as a dreamlike or unreal place and may be accompanied by poor memory of specific events.
First-degree Relative: A first degree relative is a family member who shares about 50 percent of their genes with a particular individual in a family. First degree relatives include parents, offspring, and siblings.
Genetics Home Reference
Obsessive-compulsive Disorder: Obsessive-compulsive disorder is an anxiety disorder in which people have unwanted and repeated thoughts, feelings, ideas, sensations (obsessions), or behaviors that make them feel driven to do something (compulsions).
A.D.A.M. Medical Encyclopedia
Post-traumatic Stress Disorder: A common anxiety disorder that develops after exposure to a terrifying event or ordeal in which grave physical harm occurred or was threatened.
Slow-wave sleep: state of deep usually dreamless sleep that occurs regularly during a normal period of sleep with intervening periods of REM sleep and that is characterized by delta waves and a low level of autonomic physiological activity—called also non-REM sleep, NREM sleep, orthodox sleep, S sleep, synchronized sleep.