Gathered there, they condense in the cold brain and flow downward, driving warmth in front of them.
Because of the rising vapours the head becomes thick and the eyes close; sleep occurs when the condensed vapours flow downward again and push warmth into the lower part of the body.
She then incorporates the knocking at the gate, which occured at the same time.
Ordinarily in sleep-walking dreams, events of the day come into the following night's deep sleep, but Lady Macbeth incorporates events that occured weeks, if not months, before.
This inability to see has been reported in animals: arousal from slow-wave sleep produces long periods of inhibition of the primary visual cortex, confirming Broughton's hypothesis of 'changes in later visual-evoked potential components suggesting inhibitions or occlusions of visual pathways'.
Many of the motor acts that sleep-walkers perform are based on recently performed activities.
The Doctor of Physic in Macbeth has been watching for several nights before he observes Lady Macbeth's sleep-walking, although the waiting gentlewoman has seen it more frequently (and also noted her sleep-talking).
The 'Good Doctor', who confesses that Lady Macbeth's illness is beyond his practice is well aware that sleep walking seldom leads to accidental death ('I have known those which walked in their sleep who have died holily in their beds') - but as a careful clinician he sees that Lady Macbeth is deeple depressed and fears for her suicide: 'look after her, / Remove from her the means of all anoyances / And still keep eyes upon her'.
For Galen, the direct cause of sleep was the lack of animal spirits in the somatic and kinetic organs.
During the digestion of food or physical exhaustion a kind of misty diathesis rises from the inner part of the body to the brain, and entails the quiteude of most of the body.
Indeed, in her very first appearance in the play, she is shown reading the letter from Macbeth that contains the prophesy of the Weird Sisters.
Moving and vivid are the hand-washing gestures of Lady Macbeth during her sleep-walking, in her last appearance of the play, with the words 'Yet who whould have thought the old man had so much blood in him' - a reliving of her observation of the King's bloody corpse when she returned to Duncan's chamber to leave the daggers Macbeth had used for the murder and to 'smear the sleepy grooms with blood'.
Psychologists, physiologists and sleep researchers cannot tell us which psychic forces lead to the differing disorders of sleep.