Dolphins sleep with one eye open.
When the D-Day forces landed, Hitler was asleep. None of his generals dared send re-enforcements without his permission, and no-one dared wake him.
Drinking caffeine in the evening delays our brain's release of melatonin and interrupts our circadian rhythm by as much as 40 minutes.
40% of adult Americans have always slept on the same side of the bed.
The average person in France sleeps 8.83 hours per day, the most in the developed world.
8% of Americans sleep naked.
In darkness, most people eventually adjust to a 48-hour cycle: 36 hours of activity followed by 12 hours of sleep. The reasons are still unclear.
Koalas sleep up to 20 hours a day.
Morphine derives its name from Morpheus, the god of sleep and dreaming in Greek Mythology, for its tendency to cause sleep.
Giraffes only need 5 to 30 minutes of sleep in a 24-hour period.