Lady Macbeth is famous for it, children often do it, and it can be used in defence of murder. Sleepwalking can also be fatal - if you do it in an unfamiliar place, writes Ian Kilroy
Doctor: You see, her eyes are open.
Gentlewoman: Ay, but their sense is shut.
- Macbeth, Act V, Scene I
Recently, at three in the morning, I was woken up by a man in his boxer shorts banging on my door. I looked through the security-viewing hole that offered a vista of the hall outside my apartment, and there he was, a man standing casually in his underwear: "I need help," he said.
It turned out that the man had risen in his sleep, left his flat, and closed the door behind him. He had just moved into the flat and was in a strange environment. Thrown by his new surroundings, he had suffered a bout of somnambulism - more commonly known as sleepwalking.
But what was slightly comic in this case has been tragic in others. In Cork, in 1996, a young man died after rising in his sleep and walking through a large bedroom window, falling to his death in the garden below. A few years ago, a British tourist on a package holiday died after a fall from his hotel balcony while sleepwalking. There have also been crimes committed by sleepwalkers who have used their somnambulism as a legal defence: the man in England who raped a woman while claiming to have been sleepwalking in 1996, for example, or the man who murdered an 18-month-old boy in Dublin recently, using as his defence "sane automatism" or a kind of sleepwalking.
The reason for such a defence is based on reasoning akin to Lord Denning's in Bratty v A-G (Northern Ireland) where the judge reasoned: "No act is punishable if it is done involuntarily . . . an act which is done by the muscles without any control by the mind . . . such as concussion or whilst sleepwalking".
But what exactly is sleepwalking, and how common is it?
"Sleepwalking is an arousal from deep sleep," says Dr Catherine Crow, a sleep specialist at the Mater Private Hospital in Dublin. "Ordinary sleepwalking generally occurs during the first third of the night, when there's a lot of deep sleep. The arousal may come because of a full bladder. The person then goes into a lighter sleep, but doesn't actually come out of sleep; they move around," she says.
While sleepwalking is quite common among children, it is more unusual among adults. About 15 per cent of children aged between five and 12 sleepwalk at least once, with only 3 to 6 per cent sleepwalking more than once. While most people grow out of sleepwalking, some somnambulists do continue to night-walk into adulthood. Yet only about 2.5 per cent of adults sleepwalk, says Dr Crowe, adding that it is unusual for someone to start sleepwalking later in life.
In general, episodes involve the somnambulist rising and walking around the room. Children, in particular, might urinate in an inappropriate place, like a drawer or in the corner of their bedroom, says Dr Crowe, while others may wander to the bathroom or around the the house. While Dr Crowe says that the most extensive night-time wandering of any of her patients has been to the road outside their house, she is aware of more serious cases.
"There have been people that have driven somewhere asleep. In general, when people are asleep, they will keep to fairly simple tasks - driving is obviously a much more complicated task, but there have been people that have done it," she says.
One case in the US, for example, involved a policeman rising during the night, getting into his car and driving his route to work. When he became conscious, he was sitting in his car outside his place of work. The reason for these night excursions cannot be put down to one cause.
"Being sleep-deprived can lead to sleepwalking if you tend to sleepwalk as an adult," says Dr Crowe. "It's on the night after you've had little sleep that you'll sleepwalk, on your catch-up, when you have more deep sleep. Also, if you've taken a lot of alcohol you're probably more likely to sleepwalk. However, a little alcohol might make you less likely to."
The fact that sleepwalking only occurs in deep, non-REM or dream sleep, is what accounts for the somnambulist's ability to move. In REM sleep, our muscles normally lock to protect us and others from acting out our dreams. However, as we have the use of our muscles in non-dream, non-REM sleep, we have the ability to rise, perform tasks and wander.
"Some would say that people who continue to sleepwalk into adulthood are people who are anxious or people with psychological issues that haven't been resolved," says Dr Crowe. "While not everybody that I see has psychological issues, I have to say that a lot of them do . . . not necessarily depressed, but with unresolved issues from childhood. Often when they see a psychologist the frequency of their sleepwalking goes down," she says.
There are times when people prone to sleepwalking should exercise extra care, says Dr Crowe. "When on holiday, extra care should be taken. If you're used to sleeping in your own room with the door on the right and the bathroom on your left and on holiday you're in a room with an open balcony on your left, then you should be very careful. You might wander to the balcony where normally you would find your bathroom," she says.
While there is no cure for sleepwalking, there are some practical steps that can be taken to manage it. For children, a regular sleep routine with enough sleep is the most important thing. Limiting the amount of liquids they take before bedtime may also help, preventing the trigger of a full bladder which can provoke an arousal.
Where sleepwalking persists, common-sense measures should be taken, such as locking the child's bedroom window and putting a security gate at the top of the stairs to prevent a fall. A bell could also be placed on the child's bedroom door, alerting a parent if the child should leave the room. What is most important to remember is that sleepwalking is so common among children that it is in no way abnormal, and that it will more often than not disappear with time.
"In terms of adults who sleepwalk; they should talk to their GP about it. Observing good sleep hygiene will help, like avoiding coffee and stimulants in the hours before bed and keeping regular hours. But even in adults, sleepwalking disappears with time. You get people sleepwalking in their 20s, fewer people sleepwalk in their 30s, and very few sleepwalk in their 40s. Like children, adults grow out of it," says Dr Crowe.
If you are afflicted by night wanderings, however, it may be of some comfort to know that you're in some pretty prestigious company - company other than that most famous of sleepwalkers, Lady Macbeth. Not only did Elvis Presley sleepwalk as a young man, but Friends star, Jennifer Aniston is another fellow somnambulist. She recently set off her house alarm sleepwalking, to the consternation of her husband Brad Pitt, who found her heading in the direction of the swimming pool - a reminder of the potentially tragic consequences of somnambulism.
As for my neighbour wandering around in his boxers, in the end we had to break down the door to get him back to bed.