Also in this week's column:

• Great moments in human research 1
• Does urinating after sex prevent catching HIV or other infections?
• How much damage does a tapeworm do to the human body?

Is it dangerous to wake a sleepwalker?

Asked by Gale Power of Manly, NSW, Australia

It is a myth that it is dangerous to wake up a sleepwalker because it may cause them a heart attack, shock, brain damage, or something else. It is not a myth that it is dangerous to wake up a sleepwalker because of the possible injury the sleepwalker may inflict upon themselves or the person waking them up.

According to Dr Giuseppe Plazzi of the Department of Neurological Sciences at the University of Bologna in Italy, rousing a sleepwalking person, especially vigorously, might confuse or distress them temporarily. Disoriented, they may strike out at anyone close. It is best not to be in their way.

Instead, it might be better to simply guide them back to bed in their sleep. It is not likely that a sleepwalker when woken up suddenly will have a cardiac event. It is no different from when a person sleeping normally is suddenly awakened by, say, a loud noise. The important thing is to protect a sleepwalker from themselves.

Dr Plazzi and four colleagues recently reviewed research on sleepwalking in the December 2005 issue of Neurological Sciences. According to the Plazzi study:

• Sleepwalking is surprisingly common. Thirty per cent of children between the ages of five and 12 experience at least one sleepwalking episode. Persistent sleepwalking occurs in between one to six per cent of children. Sleepwalking peaks at between ages four and six.
• Sleepwalking occurs occasionally in two to three per cent of adults. About one in every 250 adults sleepwalks once a week.
• The prime time for sleepwalking is about one to 2-3 hours into sleep.
• Sleepwalking tends to run in families.
• Stress may be the most common reason for sleepwalking. Other causes in adults include sleep deprivation, alcohol intake, and drug intake.
• People sometimes perform elaborate tasks while sleepwalking.
• When sexual activity takes place while sleepwalking, it is called somnambulistic sexual behaviour, sleepwalking sexual behaviour, or sexsomnia.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au