1. We spend a third of our lives sleeping.

2. A complete sleep cycle takes between 90 and 110 minutes on average. About 75% of that cycle takes place in the four non-REM (rapid eye movement) stages, and the rest in the REM stage. It’s vital to go through all the stages to feel refreshed. If your cycle is interrupted before the final stage, you have to go back and start all over again.

3. Humans are the only mammals that willingly delay sleep.

4. Infants generally need about 16 hours of sleep a day.

5. Babies can cause their parents to lose about 400 to 750 hours of sleep in the first year.

6. Seventeen hours of sustained wakefulness leads to a decrease in performance equivalent to a blood-alcohol level of 0,05 percent.

7. The involuntary muscle spasms we sometimes experience just before we fall asleep are known as hypnic jerks.

8. Sea otters join paws when they sleep so they don’t drift away.

9. According to the US National Institute of Neurological Disorders and Stroke, if you don’t sleep your neurons become so depleted of energy and so polluted with the by-products of normal cellular activities that they begin to malfunction.

10. Your immune system also needs time out. Research has shown that when you’re sleep-deprived your immune system reacts in the same way as when you’re under stress. Over time this can compromise your health and make you more susceptible to infection.