Encephalitis lethargic
An epidemic form of encephalitis (brain inflammation). However there has been no major outbreaks of the conditions since the 1920’s, but rare sporadic cases still happen. Symptoms of encephalitis lethargic are those of encephalitis, with drowsiness and additional lethargy.
A great number of survivors if the initial illness during big epidemics developed a movement disorder that became known as post-encephalitic Parkinson’s disease.