T.S. Eliot was under the strain of a troubled marriage and had been in psychotherapy when he wrote The Waste Land, a poem the language of which displays disintegration and irrationality.
According to Freudian psychology-based psychoanalytic criticism, the meaning of the text of The Waste Land encompasses the psyche of the author, T.S. Eliot. Marwa Makram Attiya, in T.S. Eliot's The Waste Land, According to Psychoanalytic Criticism, translates the Epigraph at the head of The Wasteland as stating that the Sibyl from mythology was hanging in a cage and when asked what she wanted, retorted, "I want to die." According to Freudian theory as expounded in psychoanalytical criticism, this adheres to the Freudian principle of a death drive, also known as a death wish.
This death theme is carried out from the beginning of The Waste Land and incorporates themes of cold burial and void. Eliot's Freudian alter ego (the textual representation of a creative author's self), the narrator, speaks of burying memories under cold blankets of snow, which symbolizes the cold sod of earth that covers memories in death. The void of death is symbolized as the empty sea. This symbolism is enhanced when Madam Sosostris presages his death by water: The present and future burying of memorable life in a void. Psychoanalytically, this reflects Eliot's state of mind regarding a life of memories he seeks to bury and the void he feels his life to be, which correlates with the Freudian death drive.
The Waste Land then transitions into a scene in London where the foregoing themes and symbols are enhanced further by the narrator's conversation with Stetson. The end result of the conversation is the pronunciation that everything, symbolized by Stetson's crop, is dead and that dead things can never grow and bloom. The narrator's conclusion, as expressed in his final remarks, underscores the Freudian death drive evident all through The Wasteland. Eliot's Freudian alter ego narrator states that all who believe that life can thrive and bloom are hypocrites because all is dead, and death, a void, cannot live or bloom.
Harry Trosman in After The Waste Land: Psychological Factors in the Religious Conversion of T. S. Eliot states:
The Waste Land was...the product of a period of severe psychological distress in the life of [T.S. Eliot]. The poem was mostly written in 1921...During the previous two or three years, Eliot had been exhausted, depressed, anxious, hypochondriacal and he dreaded a psychotic disintegration. [He] was unable to continue to work. He obtained a three-month leave of absence...to enter psychiatric treatment...The events leading up to his illness, the psychological reactions which ensued, the psychopathology, the nature of the psychotherapy and the probable effects of these factors on the composition of The Waste Land have been described in a recent publication (Trosman, 1974).
[Also see T.S. Eliot's The Waste Land, According to Psychoanalytic Criticism, by Marwa Makram Attiya, which was a source for my remarks.]
This is just a mild and humble addition to the first answer. There are essays exploring the narratorial position in Waste Land with the Lacanian theory in the context. The Lacanian knotting of Real, Imaginary and Symbolic can be used as a critical grid and from this perspective, the poem might be seen enacting a movement from the imaginary to the symbolic, with language being foregrounded (imaginary, just a heap of broken images). But rather mystically it also grapples with the beyond of language, the Real as the silence of the Hyacinth girl or the pure-sounds of drip-drop-drop or coco-rico suggest.
The poem foregrounds the idea of the unconscious-speech in its stress on lack of chronology and break from rationality.
Repression of the sexual is a major theme in the poem especially in the 'hurry up please it's time' episode and so on.
The breakdown of the ego and an opening into the chaos of subjectivity is the fundamental experiential position from which the poem is narrated.