The Sandman is an 1816 short story by E.T.A. Hoffmann. This story has been the subject of much discussion and interpretation, including by Freud. You can read it online with illustrations here. You can listen to it here. It begins,
NATHANEL TO LOTHAIRE
Certainly you must all be uneasy that I have not written for so long - so very long. My mother, am sure, is angry, and Clara will believe that I am passing my time in dissipation, entirely forgetful of her fair, angelic image that is so deeply imprinted on my heart. Such, however, is not the case. Daily and hourly I think of you all; and the dear form of my lovely Clara passes before me in my dreams, smiling upon me with her bright eyes as she did when I was among you. But how can I write to you in the distracted mood which has been disturbing my every thought! A horrible thing has crossed my path. Dark forebodings of a cruel, threatening fate tower over me like dark clouds, which no friendly sunbeam can penetrate. I will now tell you what has occurred. I must do so - that I plainly see - the mere thought of it sets me laughing like a madman. Ah, my dear Lothaire, how shall I begin ? How shall I make you in any way realize that what happened to me a few days ago can really have had such a fatal effect on my life? If you were here you could see for yourself; but, as it is, you will certainly take me for a crazy fellow who sees ghosts. To be brief, this horrible occurrence, the painful impression of which I am in vain endeavoring to throw off, is nothing more than this - that some days ago, namely on the 30th of October at twelve o'clock noon, a barometer-dealer came into my room and offered me his wares. I bought nothing, and threatened to throw him downstairs, upon which he took himself off of his own accord.
Only circumstances of the most peculiar kind, you will suspect, and exerting the greatest influence over my life, can have given any import to this occurrence. Moreover, the person of that unlucky dealer must have had an evil effect upon me. So it was, indeed. I must use every endeavor to collect myself, and patiently and quietly tell you so much of my early youth as will bring the picture plainly and clearly before your eyes. As I am about to begin, I fancy that I hear you laughing, and Clara exclaiming, 'Childish stories indeed!' Laugh at me, I beg of you, laugh with all your heart. But, oh God! my hair stands on end, and it is in mad despair that I seem to be inviting your laughter, as Franz Moor did Daniel's in Schiller's play. But to my story.