At the end of world war I, a strange new illness arose in Eastern Europe. The sleeping sickness, encephalitis lethargica, spread around the globe, and its complications attracted the interest of neurologists. Usually headache, nausea and fever were followed, often within one day, by sleeping that frequently occurred in the most uncomfortable positions. Among the late sequelae, post-encephalitic parkinsonism was particularly common.
Emotions are scarcely noticeable in the face, but they are mentally intact.
This disease also causes double vision, trouble swallowing, and drooling. After around 1920, the disease almost completely disappeared. Many believe that it was associated with the 1918 Spanish flu epidemic, and researchers are still looking for a connection. The viral agent was never identified, the clinical and pathologic features were typical of viral infection, it is often recognized as the first slow virus infection of the nervous system in human beings. It eventually struck perhaps five million people.