Mental breakdown and death (1889–1900)

On 3 January 1889, Nietzsche suffered a mental collapse. Two policemen approached him after he caused a public disturbance in the streets of Turin. What happened remains unknown, but an often-repeated tale from shortly after his death states that Nietzsche witnessed the flogging of a horse at the other end of the Piazza Carlo Alberto, ran to the horse, threw his arms up around its neck to protect it, and then collapsed to the ground.
In the following few days, Nietzsche sent short writings—known as the Wahnbriefe ("Madness Letters")—to a number of friends including Cosima Wagner and Jacob Burckhardt. Most of them were signed "Dionysos", though some were also signed "der Gekreuzigte" or "the crucified one". To his former colleague Burckhardt, Nietzsche wrote: "I have had Caiaphas put in fetters. Also, last year I was crucified by the German doctors in a very drawn-out manner. Wilhelm, Bismarck, and all anti-Semites abolished." Additionally, he commanded the German emperor to go to Rome to be shot and summoned the European powers to take military action against Germany.
On 6 January 1889, Burckhardt showed the letter he had received from Nietzsche to Overbeck. The following day, Overbeck received a similar letter and decided that Nietzsche's friends had to bring him back to Basel. Overbeck travelled to Turin and brought Nietzsche to a psychiatric clinic in Basel. By that time Nietzsche appeared fully in the grip of a serious mental illness, and his mother Franziska decided to transfer him to a clinic in Jena under the direction of Otto Binswanger. In January 1889, they proceeded with the planned release of Twilight of the Idols, by that time already printed and bound. From November 1889 to February 1890, the art historian Julius Langbehn attempted to cure Nietzsche, claiming that the methods of the medical doctors were ineffective in treating Nietzsche's condition. Langbehn assumed progressively greater control of Nietzsche until his secretiveness discredited him. In March 1890, Franziska removed Nietzsche from the clinic and, in May 1890, brought him to her home in Naumburg. During this process Overbeck and Gast contemplated what to do with Nietzsche's unpublished works. In February, they ordered a fifty-copy private edition of Nietzsche contra Wagner, but the publisher C. G. Naumann secretly printed one hundred. Overbeck and Gast decided to withhold publishing The Antichrist and Ecce Homo because of their more radical content. Nietzsche's reception and recognition enjoyed their first surge.
In 1893, Nietzsche's sister Elisabeth returned from Nueva Germania in Paraguay following the suicide of her husband. She read and studied Nietzsche's works and, piece by piece, took control of them and their publication. Overbeck eventually suffered dismissal and Gast finally co-operated. After the death of Franziska in 1897, Nietzsche lived in Weimar, where Elisabeth cared for him and allowed visitors, including Rudolf Steiner (who in 1895 had written one of the first books praising Nietzsche), to meet her uncommunicative brother. Elisabeth at one point went so far as to employ Steiner as a tutor to help her to understand her brother's philosophy. Steiner abandoned the attempt after only a few months, declaring that it was impossible to teach her anything about philosophy.
Nietzsche's mental illness was originally diagnosed as tertiary syphilis, in accordance with a prevailing medical paradigm of the time. Although most commentators regard his breakdown as unrelated to his philosophy, Georges Bataille dropped dark hints ("Man incarnate' must also go mad") and René Girard's postmortem psychoanalysis posits a worshipful rivalry with Richard Wagner. Nietzsche had previously written, "all superior men who were irresistibly drawn to throw off the yoke of any kind of morality and to frame new laws had, if they were not actually mad, no alternative but to make themselves or pretend to be mad" (Daybreak,14). The diagnosis of syphilis has since been challenged and a diagnosis of "manic-depressive illness with periodic psychosis followed by vascular dementia" was put forward by Cybulska prior to Schain's study. Leonard Sax suggested the slow growth of a right-sided retro-orbital meningioma as an explanation of Nietzsche's dementia; Orth and Trimble postulated frontotemporal dementia while other researchers have proposed a hereditary stroke disorder called CADASIL. Poisoning by mercury, a treatment for syphilis at the time of Nietzsche's death, has also been suggested.
In 1898 and 1899 Nietzsche suffered at least two strokes which partially paralyzed him, leaving him unable to speak or walk. He likely suffered from clinical hemiparesis/hemiplegia on the left side of his body by 1899. After contracting pneumonia in mid-August 1900, he had another stroke during the night of 24–25 August and died at about noon on 25 August. Elisabeth had him buried beside his father at the church in Röcken bei Lützen. His friend and secretary Gast gave his funeral oration, proclaiming: "Holy be your name to all future generations!" Nietzsche had written in Ecce Homo (at that point still unpublished) of his fear that one day his name would be regarded as "holy".
Elisabeth Förster-Nietzsche compiled The Will to Power from Nietzsche's unpublished notebooks and published it posthumously. Because his sister arranged the book based on her own conflation of several of Nietzsche's early outlines and took great liberties with the material, the scholarly consensus has been that it does not reflect Nietzsche's intent. (For example, Elisabeth removed aphorism 35 of The Antichrist, where Nietzsche rewrote a passage of the Bible.) Indeed, Mazzino Montinari, the editor of Nietzsche's Nachlass, called it a forgery.