Stanford study says that more than 8.4 million people in U.S. or about 3.6 percent of the population are prone to sleepwalking, also known as somnambulism.

“Apart from a study we did 10 years ago in the European general population, where we reported a prevalence of 2 percent of sleepwalking. There are nearly no data regarding the prevalence of nocturnal wanderings in the adult general population in the United States, the only prevalence rate was published 30 years ago,” the researchers wrote.

For the study, the researchers analyzed sleeping habits of some 19,000 adults. The participants were asked about their health, medication and sleep walking in telephonic surveys.

30 percent of the respondents reported to have sleepwalked during the past year.

Reports say that depression ups the risks of sleepwalking by 3.5 percent.

"There is no doubt an association between nocturnal wanderings and certain conditions, but we don't know the direction of the causality. Are the medical conditions provoking sleepwalking, or is it vice versa? Or perhaps it's the treatment that is responsible,” Dr. Maurice Ohayon, lead author of the study said.

"You have a two and a half times higher chance of sleepwalking if you are taking an over-the-counter sleeping pill with diphenhydramine," Ohayon said to WebMed.

Jan Brandes, a neurologist at Vanderbilt University in Nashville, said that the research shows that sleepwalking is not taken as seriously. She advised people to keep track of their sleep and consult their doctor if they sleepwalk, USA NEWs reported.

"But most of us would say going to bed at 10 and waking up at 6 — rather than roaming the house — would be the ideal," she said.

The present study also found that 2.6 percent of the respondents had between 1 and 12 episodes of sleepwalking during the past year; 1 percent reported to have 2 or more episodes of sleepwalking in a month.

Previous studies have found co-relation between nocturnal wandering to increased drowsiness in the morning.

“These patients [sleepwalkers] were more likely to present with sleep-related eating features, comorbid insomnia, had and lifetime usage of non-benzodiazepine hypnotics, especially zolpidem. A heightened awareness of the presence of sleepwalking and their associated risk factors among the adult psychiatric population is needed,” report Siu –Ping Lam and colleagues in the Australian and New Zealand Journal of Psychiatry. Their study focuses on the factors like psychopathology and medication and onset of sleepwalking in adult population.

PubMed says that awakening people who are wandering around the house is okay and although they may become disoriented for a while, it won’t harm them. It also says that people can get injured while walking and it is helpful to remove all electrical cords or move furniture to prevent injuries.

The present study is published in the journal Neurology.

Cases involving sleepwalkers

In 1981, Arizona man Steven Steinberg pleaded not guilty for the murder of his wife Elena on the grounds that he was sleepwalking. Elena was stabbed with a kitchen knife 28 times.

In another case in 1987, Kenneth Parks( Toronto) drove nearly 23 kilometers , killed his mother-in-law, assaulted his father–in-law, slashed his own wrists and confessed his crime at a police station, all while apparently sleepwalking.