"I told you not to mix NyQuil and Ambien!"
It's not the first act of a horror movie, but a real, baffling disease that had doctors puzzled at the beginning of the 20th century. It's called encephalitis lethargica, or the sleeping sickness, and it struck the world as an epidemic just after the Spanish flu died down. Nobody has any idea where it came from or where it went.
It began with victims complaining of a sore throat, right before it escalated into a goddamned living nightmare, the victims afflicted with hallucinations and madness before their bodies ultimately locked up. While sufferers appeared to be asleep, they were actually fully conscious but unable to move. Many died during this stage, but for those who recovered, the nightmare was far from over.
"After discussing what a pain in the ass recovery will be, his father and I have decided to pull the plug."
Survivors of the sleeping disease suffered horrifying behavioral problems for the rest of their lives, becoming excessively violent and -- regardless of gender -- somewhat rapey. On top of all this, they became emotionally indifferent, unable to recognize, for example, the beauty of art. Ten years after the epidemic struck, new cases suddenly stopped appearing, its only legacy being the alien clones it left behind.
Nearly a century later, doctors still don't know what the hell was going on there, although they realize it was some kind of brain thing. One hypothesis is that the bacteria that caused the sore throat triggered an immune response that also destroyed parts of the brain, but many scientists still think a virus is the more likely culprit.