I'm an ardent student of history. And I know that most here probably think the history of the Middle Ages is a sure-fire cure for insomnia. But we can learn a lot that is important for today's day and age, by studying the past.
Medieval historian Norman F. Cantor has written much about the plagues of the Middle Ages, and especially the "Black Death". It had 3 forms: the bubonic (with the familiar swellings), the septicemic (where the blood is infected), and the pneumonic (involving the lungs). Of these, septicemic and especially the pneumonic form are the worst. Because they don't require a vector (such as fleas) for transmission. The septicemic is spread by contact with bodily fluids, such as blood and sputum. However the "pneumonic" form of plague is the most contagious, because it can be spread directly from person to person by coughing. (Just like flu and colds are spread).
He ends his book with the chilling observation:
"In today's world, we think the horrors that our distant ancestors endured from the Black Death, are a relic of the past. Something that our modern medical science has conquered, never to be seen again. Nothing could be further from the truth. The Plague is merely lingering, dormant. Biding its time. Waiting for the opportunity to once again be unleashed on an unsuspecting humanity."