Is Sleepwalking Normal?
"Sleepwalking" is a blanket term that applies to any complex activity, from talking to doing parts of your daily routine, while you are still asleep. The episodes occur in the stages of slow-wave sleep, which is why they generally occur in the first third of the night. Similar behaviors that occur during REM sleep are referred to as REM sleep behavior disorders. 
What Is the Prevalence of Sleepwalking?
The data gathered on the prevalence of sleepwalking in the general population is unclear with some reporting data as low as 1% while others place that number as high as 15%.  In an attempt to gather updated, more accurate data, researchers at Stanford University sampled nearly twenty-thousand people determining that this number is actually higher than previously reported. According to their research, nearly 30% of the population has experienced sleepwalking episodes at some point in their lives. The number of adults that had recent sleepwalking episodes was also higher than the >1% previously reported. The current study places this number closer to 4%. 
Who Is Affected?
Children make up the lion's share of those that experience sleepwalking episodes. They occur equally between boys and girls. Sleepwalking episodes can begin as soon as a child is able to walk then generally subside following adolescence.  Genetics is also a risk factor for determining the likelihood of sleepwalking. Research indicates that the risk increases in direct relation to which parents are affected. The risk increases by 45% if one parent is affected and to 60% if both parents are affected.  If the larger family unit is taken into consideration, a person that has a first-degree relative that is affected by sleepwalking is ten times more likely to be affected as well. 
Are There Risk Factors?
Fatigue, anxiety and seizure disorders are known triggers of sleepwalking episodes, but the story does not end there.  In the Stanford University study, researchers identified several more factors that can contribute. Individuals with depression or obsessive-compulsive disorder are up to four times more likely to sleepwalk.  Alcohol and certain medications can also trigger a sleepwalking episode including thioridazine hydrochloride, chloral hydrate, lithium carbonate, prolixin, perphenazine, and desipramine hydrochloride. 
The Influence of Ambian®
People that use the prescription sleep aid zolpidem, also called Ambian®, report instances of sleepwalking, eating, and even driving. While there is no hard information on who is likely to develop this bizarre side effect, scientists at the Georgetown University Medical Center have identified the properties of zolpidem that trigger the episodes. While zolpidem helps the brain shut down and sleep, it also triggers other parts of the brain that would normally be "turned off" during sleep. Why it does this is unknown, but sleepwalking can definitely be triggered by zolpidem use. 
Should I Be Worried?
Sleepwalking is peculiar but largely harmless. However, contact your doctor if you are doing potentially dangerous activities, such as driving, while asleep, have frequent episodes or have other symptoms as well.