Sleepwalking can occur at different phases of sleep. In deep sleep phase or non-rapid eye movement phase, sleepers are sometimes capable of performing quite complex actions without the involvement of their conscious mind - the conscious mind does not therefore recall the events of the previous night. Sleepwalking during the rapid eye movement phase of sleep is less common.

It is during this phase of sleep that we have vivid life-like dreams. In people with REM behavioural disorder, the body is not paralysed during the dream and they are able to act out their dreams which are often violent. Unlike deep sleepwalkers, these people usually remember the dreams clearly the next day. For example, one man ran head on into his dresser whilst dreaming he was tackling an opponent in football!

Men are more likely to sleepwalk that women.

'I have seen her rise from her bed, throw her nightgown upon her, unlock her closet, take forth paper, fold it, write upon it, read it, afterwards seal it, and again return to bed; yet all this while in a most fast sleep.'
Macbeth Act V Scene 1

The lady seen sleep-writing is the infamous Lady Macbeth. She begins to sleepwalk as the guilt she has repressed for her role in the murder of King Duncan erupts into her dreams. Lady Macbeth is observed walking down the hall with a lantern, rubbing her hands roughly in an attempt to remove the bloody stain which seems never to go away.

She begins to reveal, while still asleep, the depth of her guilt and subsequent slide into madness and suicide. In myth and reality, sleepwalking is often considered to represent feelings denied in consciousness that bubble up through sleep.

Mundane factors are known to trigger sleepwalking episodes in people, like alcohol or stress.

'There on our favourite seat, the silver light of the moon struck a half-reclining figure, snowy white. The coming of cloud was too quick for me to see much …, but it seemed to me as though something dark stood behind the seat where the white figure shone, and bent over it…. When I bent over her I could see that she was still asleep.'
Bram Stoker's Dracula

Sleepwalking has long been tainted with the supernatural. In this extract from Bram Stoker's Dracula, the Count has the power to entice his victim to sleepwalk to the churchyard to meet him in the dead of night. The novel weaves together the themes of trance, madness and the supernatural into a veritable vampiric web.

Within the law, the condition of automatism is defined as acting involuntarily. There are two legal categories of automatism - insane automatism, considered a 'disease of the mind', and non-insane automatism which is linked to environmental influences.

One-third of your life is spent sleeping.

REM guitarist Peter Buck was acquitted of attacking BA staff on a transatlantic flight to London in 2002 on the basis of non-insane automatism. He had no recollection of the incident after combining alcohol with a sleeping pill at the start of the flight.

There are about 85 recognized sleep disorders, most of which are treatable.

Your sleep affects your mood and vice versa.

In 1998, chef Dean Sokell was jailed for life after battering his wife Eleni to death in an attack which began while he was asleep. Sokell admitted murder on the basis that he had woken up to find he was hitting Eleni with a claw hammer, but then, while awake, carried on and finally stabbed her to silence the screams.

In 2005, Jules Lowe made legal history as the first person in Britain to have been found not guilty of murder on the basis of insane automatism.