In 1603, at around the time that Shakespeare wrote Macbeth, Edward Jorden published the first book in English about hysteria, entitled A Briefe Discourse of a Disease Called The Suffocation of the Mother. In this context, "the Mother" means the womb or uterus, and "The Suffocation of the Mother" is a disease to which Jorden referred as Passio Hysterica—physical symptoms caused by hysteria.
Jorden wrote the book after he testified at the witchcraft trial of Elizabeth Jackson in 1602, where he argued, unsuccessfully, that the supposed victim of Jackson's witchcraft, fourteen-year-old Mary Glover, wasn't bewitched by Jackson's demonic or supernatural powers, but that Glover's symptoms of a swollen throat, convulsions, violent fits, and intermittent blindness were a result of Glover's own hysteria.
Jorden believed that although Glover's hysteria mimicked signs of demonic possession, her physical symptoms were caused by furor uterinus, a fury of the womb, in which the womb moved around inside the body, putting pressure on other organs, interfering with their usual function, and causing "monstrous and terrible" symptoms.
This theory has been well and truly refuted, of course, but Jorden also suggested in his book that hysteria and the resulting physical symptoms might be caused by "perturbations of the minde."
The trial was widely discussed in London at the time, and Shakespeare must have known about it. It's not known whether Shakespeare read Jorden's book, but Jorden's remarks about "perturbations of the minde" might have piqued Shakespeare's interest if he did read it.
In his plays, Shakespeare provides insight into the attitudes, values, and beliefs of his Elizabethan and Jacobean audiences. Ophelia’s seeming madness, for example, was believed to be a result of her grief over the death of her father, her unrequited love for Hamlet, or simply sexual frustration.
Shakespeare's audience likewise attributed Lady Macbeth's descent into madness to sexual frustration—although that seems unlikely to modern audiences—and, more likely, to her guilt about Duncan's murder.
In The Hysteria of Lady Macbeth, written by Isador H. Coriat, M.D. and published in 1912, the author suggests that Lady Macbeth's behavior was a result not only of guilt over Duncan's murder, but a result of sexual frustration, sublimation of her female self to stereotypical male qualities of ambition and lust for power ("unsex me here"), the desire for a child, or the memory and heartbreak of the loss of a child.
LADY MACBETH. I have given suck, and know
How tender ’tis to love the babe that milks me... (1.7.60-61)
The "Out, damned spot!" scene (act 5, scene 1) is the last time the audience sees Lady Macbeth, and this scene is often cited as the prime example and proof of Lady Macbeth's madness and hysteria.
Lady Macbeth seems delusional, and she appears to be sleepwalking, both of which are recognized symptoms of hysteria. Shakespeare's audience likely attributed this hysteria to her guilt over the deaths of Duncan, Banquo, and Lady Macduff, all of whom she mentions in the sleepwalking scene.
The modern audience member might, and often does, concur with the Jacobean audience member's interpretation of Lady Macbeth's behavior; but what Lady Macbeth exhibits with her sleepwalking and incessant hand washing isn't caused by hysteria but considered psychopathological behavior symptomatic of an underlying mental disorder.
This might better explain Lady Macbeth's all-too-abrupt transition from a strong, ambitious, take-charge woman—a true force of nature—into a weak, confused, incoherent, simple-minded sleepwalker who very soon commits suicide. Whether her behavior is caused by Jacobean hysteria or modern mental illness, Lady Macbeth is nonetheless a fascinating and compelling character.