1. Humans spend a third of their life sleeping (25 years or more).

2. Humans can survive longer without food than they can without sleep.

3. During the first two years of a baby’s life, new parents will miss six months of sleep on average.

4. In 1894, Russian scientist Marie Mikhaïlovna de Manacééne conducted one of the earliest experiments on extreme sleep deprivation. She found that when she deprived puppies of sleep, they all died within four or five days, despite every effort to keep them alive. The younger the puppy, the more quickly it died.

5. Giraffes sleep only 1.9 hours a day in five- to 10-minute sessions. Koalas, however, are the longest-sleeping mammals, sleeping up to 22 hours a day.

6. The word “sleep” derives from the Proto-European base *sleb, “to be weak,” and is related to “slack.” “To sleep around” was first recorded in 1928.

7. Sleep is a universal characteristic of complex living organisms and has been observed in insects, mollusks, fish, amphibians, birds, and mammals.

8. Only one half of a dolphin’s brain goes to sleep at a time. Dolphins are capable of what is known as unihemispheric sleep, in which one hemisphere of the brain goes into a deep sleep while the other hemisphere remains awake. This allows dolphins to sleep under water without drowning. Dolphins spend approximately one third of their lives asleep.

9. Slow-wave sleep appeared about 180 million years ago. REM sleep is believed to have appeared 50 million years later. Humans most likely developed a monophasic sleep/wake pattern in the Neolithic period (10,000 B.C.).

10. In Greek mythology, Hypnos (Somnus in Roman mythology) was the god of sleep. Thanatos, or death, was his twin. Poppies and other sleep-inducing plants grew at the entrance of Hypnos’ cave.

11. Heart disease, diabetes, and obesity all have been linked to chronic sleep loss.

12. There are at least 84 identified sleep/wake disorders.

13. During the night, we move back and forth between quiet sleep and deeper, active sleep. We go through four or five 90- to 110-minute rounds of this basic quiet/active sleep cycle each night.

14. The average amount of time people sleep has dropped from nine hours in the pre-lightbulb era to seven-and-a-half hours today.

15. Ken Parks, who murdered his mother-in-law by bludgeoning her with a tire iron and attempted to murder his father-in-law by strangulation, offered sleepwalking as a defense during his trial. He was acquitted.

16. Each year, sleep-related errors and accidents cost U.S. businesses an estimated $56 billion, cause nearly 25,000 deaths, and result in 2.5 million disabling injuries.

17. Over 70 million Americans suffer from a sleep disorder. Of those, over 60% have a chronic disorder.

18. When applied patiently and systematically, sleep deprivation is said to be the single most effective form of coercion and torture.

19. A nineteenth-century Chinese merchant was sentenced to death for murdering his wife. Sleep deprivation was deliberately chosen as the method of execution on the grounds that it would cause the maximum amount of suffering and would serve as the greatest deterrent to other potential murderers. He eventually died on the nineteenth day, having suffered terribly.

20. People whose normal nightly sleep duration is either unusually short (less than four hours) or unusually long (more than nine or 10 hours) have a higher-than-average risk of dying prematurely.

21. A person’s core body temperature drops to facilitate the onset of sleep. This means that artificial heat sources, such as electric blankets, can negatively affect a person’s quality of sleep.

22. The phenomenon of sudden, unexplained death of adults during sleep is called SUDS. In the Philippines it is known as bangungut, which literally means “to rise and moan during sleep.”

23. Sleepwalking is also called somnambulism, from the Greek somnus (sleep) + amb (to walk). Most sleepwalkers remember little, if anything, about the experience. While sleepwalking, a person can sometimes use the bathroom, eat, or even talk. Scientists postulate that adult sleepwalking has a genetic component.

24. Studies show that less sleep (six hours or less) can lead to higher inflammatory proteins in the blood.

25. Western industrialized societies have such high numbers of sleep deprivation that what is abnormal sleepiness is now considered normal.