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While most of us head to bed to sleep, perchance to dream, up to 5 per cent of adults get up to all sorts of alarming things after nodding off.
Dr Tony Fernando, Auckland University faculty of medicine psychiatrist and sleep specialist, gets to see New Zealand's worst cases of sleepwalking.
"I've encountered a few cases where men have beaten up their wives in the middle of the night - and they don't remember until the wives tell them.
"One West Auckland man kept crashing through glass doors. He'd walk through ranch sliders and needed to physically restrain himself before he went to bed.
"He's been severely cut quite a few times and ended up having to tie himself to his bed with fabric restraints.
"It's stressful on relationships because the person who sleepwalks thinks they are crazy. It's a treatable condition with anti-anxiety medication. It doesn't rid the sufferer of sleepwalking, but it reduces the severity."
Medically the condition is called somnambulism - and sufferers can do things such as get out of bed, drive a car, make a cup of tea or a meal while totally unaware of what they are doing.
Last week, a British detective investigating the death of Howick College student Ross Kimpton, 17, said it was a "tragic case of sleepwalking".
The teenager died last month while on a rugby trip after falling 25-30m from a London hotel room.
Sleepwalking trends emerge in families, says Fernando, but it's unknown if it's hereditary. "Sleepwalking is more common in children with about 15 per cent experiencing it. As the adult brain matures the circuits start to synchronise so the sleep 'switch' and wake 'switch' techniques are more firm.
"With sleepwalking adults, their switches get stuck in the middle somewhere. When they're asleep the switch will move to partial arousal but the rest of the brain is still asleep."
Most children outgrow it by their teens but 4 to 5 per cent of adults sleepwalk. Common triggers are sleep deprivation, poor quality sleep, alcohol and stress.
One of Fernando's cases involved a Northland couple who lost custody of one their children after the husband had an episode of "sex-somnia", a variation of sleepwalking of a sexual nature. The couple called health professionals after an episode involving his 6-year-old daughter. CYFs was notified and the man was charged with indecent assault.
Fernando was an expert witness at the man's trial in 2005, in which he was acquitted.
Sadly, Fernando says, the man is still unable to have contact with his daughter and the husband and wife, while still close, are unable to live together as a family.
In Kimpton's case, Fernando questions the London hotel owner disputing the sleepwalking theory: "People have a misconception sleepwalking is just walking but they are able to perform complex behaviours.
"One of my clients sleepwalked into his apartment's carpark, started driving and crashed into another car.
"Dressing up, making a meal, it's not like [sleepwalkers] are zombies crashing into walls. There are different variations because it depends how much your brain is engaged.
"I'm sure they are making mistakes when they cook - like it's not a perfect hamburger and the toast might be burnt. I don't think they'll be making spaghetti carbonara in the middle of the night - nothing too complex."
Fernando says it is possible Ross Kimpton fell off the top of a building while asleep. "He had a history of sleepwalking as a kid apparently. He was probably sleep deprived from the jet lag, the kids had been drinking and he was staying on a high floor."
Fernando recommends that anyone with a severe case of sleepwalking should see a sleep specialist.
For friends and relatives he advises if someone is a known sleepwalker and is about to jump, walk on the road or fall over, they must be tackled and made to wake up - "or sometimes you can redirect them to bed". But he warns: "Sometimes grabbing them, they might fight back...if they're still in a dream phase they might think you are a monster and beat you up."
He also advises sleepwalkers should have a ground-floor bedroom - "and make sure there are obstructions along the way between the bedroom and any roads - like a solid door".
