Around the same time of the deadly Spanish Influenza (1918-1920), there was another rampant illness that many have forgotten about. It was called Encephalitis Lethargica, which at its peak killed a million people and left millions of others paralyzed in their bodies. 

While it was dubbed the sleepy sickness it had a variety of symptoms including sore throat and seizures. Eventually, the infected person would end up in a coma or dead as it had a 40% mortality rate. But then, as mysteriously as it appeared, the epidemic ended in 1926. It is still not known what caused it and it has no cure. (Source 1 | Source 2)