In the late 1880s Hasenclever increasingly suffered from a neurological and psychiatrical condition that was not specifically diagnosed at the time. This made his political work harder and harder, and in the end impossible. In 1888 he stepped down from the Reichstag, after he had collapsed during the "Geheimbund-Prozess" ("secret society trial") in Düsseldorf. He tried to regain his health in the "Maison de la santé" (French for "house of health"), a sanatorium in Schöneberg south of Berlin. There he died, reliant on support by staff and mentally incapable, on 3 July 1889, aged 52. He did not experience the end of the anti-socialist laws and the renaming of the SAP to Social Democratic Party of Germany ("Sozialdemokratische Partei Deutschlands", SPD) a year later.