In the depths of my brain I found a faint memory of a disease A that cures disease B (by raising the body temperature, I think). Disease A is fatal (or at least it was at the time) so you only get to enjoy your newfound freedom from disease B for so long. Both diseases are "old", so to speak, and this curious interaction was known as early as the 19th, maybe even 18th century. I think I may have read about it first in some classical novel. I thought disease A was malaria or sleeping sickness but a cursory search came up empty. Insomnia may or may not be one of the symptoms of disease A. Pic probably unrelated.