Psychoanalytical theory (originated by Sigmund Freud) examines the manifestation of issues which arise from a person's subconscious. According to Lois Tyson, In Critical Theory Today, Freud believed that "the notion that human beings are motivated, even driven, by desires, fears, needs, and conflicts of which they are unaware." Based upon this, one could easily apply Psychoanalytical analysis to Shakespeare's Macbeth and Lady Macbeth.
A question to ask when examining a text using Psychoanalysis are:
How can characters' behavior, narrative events, and/or images be explained in terms of psychoanalytic concepts of any kind (for example...fear or fascination with death, sexuality - which includes love and romance as well as sexual behavior - as a primary indicator of psychological identity or the operations of ego-id-superego)?
Based upon this question, one can see that Lady Macbeth's behavior is not common. Her inability to recognize the seriousness of her part in the murder of Duncan is highlighted, and compounded, in her following dialogue with Macbeth:
A little water clears us of this deed (II,ii,64).
For Lady Macbeth, the murder of Duncan is as dismissible as simply running a little water over one's hands to rinse them off.
Later in the play, Lady Macbeth's unknown, to her, conflict abruptly rises to the surface. She is seen sleepwalking and trying to rub a "spot" off of her hand.
Out, damned spot! out, I say (V,i, 35)!
Here, her unconscious (the superego) has overpowered her conscious (the id and the ego). Even the doctor, who has been sent to examine her, finds that
Foul whisperings are abroad. Unnatural deeds
Do breed unnatural troubles; infected minds
To their deaf pillows will discharge their secrets (V,i,71-73).
In the end, it is the suppressed behavior of Lady Macbeth which comes to the surface to reek havoc on her life and lead to her death. Only the application of Psychoanalytical analysis takes into consideration the subconscious of a character and, therefore, can be an appropriate lens with which the examine the character of Lady Macbeth.
Freud theory can be applied to Lady macbeth because we can find it "sleep walking Scene". Before that we should know theory of Freud he divided the mind Id, Ego, Super Ego. Here Lady Macbeth's stage is in super Ego, that uncouncious mind she walked at night. She mentaly affected because she was not take care of her husband , Macbeth, so that she alone in the castle even she was queen. Duncan's murder haunting her mind. She was disturbed by the murder even she try to overcome that level. But her all attempt failed and she psycologically affected which is not cured by the doctor.
She sucide herself because of her mental affect. It may apply to the Freud's theory.