13. Drunk and sleep. Going 17 hours without sleep impairs you to the same level as a blood alcohol-level of .05 percent, not far removed from the legal driving limit of 0.08.

14. Accidents and causes. Australian motorists’ association NRMA estimates that fatigue is involved in one in six fatal traffic accidents.

15. Our inner alarm. The “natural alarm clock” that allow some people to wake themselves up at will is caused by a burst of the stress hormone adrenocorticotropin. It’s thought to be an unconscious anticipation of the stress of waking up.

16. Obesity and fat. Failing to get enough sleep can interfere with eating habits and insulin production, making it a contributing factor in obesity and high blood glucose.

17. Disruption of sleep. It takes only a small amount of light–even the light from a digital alarm clock–to disrupt the sleep cycle.

18. Heat and sleep. Body temperature and the brain’s sleep-wake cycle are closely linked, which is why it’s hard to fall asleep in a hot room.

19. Added punch. Sleep deprivation makes the effect of alcohol more powerful .

20. Treat nightmares. Techniques of lucid dreaming–in which the sleeper is aware that they’re dreaming and can even control the action of the dream–have been used to treat nightmares.