For seven or eight hours per day, we go into a profoundly different state - a system shutdown. But how much do you really know about sleep, about why we need it and what happens while we have our nightly shuteye?

Over 60% of women experience problematic sleep (NSF 2007) and without a full sleep cycle, the skin's ability to fight premature aging is compromised.

A new baby typically results in 400-750 hours lost sleep for parents in the first year. Seventeen hours of sustained wakefulness leads to a decrease in performance equivalent to a blood alcohol-level of 0.05%.

The 1989 Exxon Valdez oil spill off Alaska, the Challenger space shuttle disaster and the Chernobyl nuclear accident have all been attributed to human errors in which sleep-deprivation played a major role.

One in 6 fatal road accidents is caused by fatigue and lack of sleep. Some studies suggest women need up to an hour's extra sleep a night compared to men, and not getting it may be one reason women are much more susceptible to depression than men.

Diaries from the pre-electric-light-globe Victorian era show adults slept nine to 10 hours a night with periods of rest changing with the seasons in line with sunrise and sunsets.

The extra-hour of sleep received when clocks are put back at the start of daylight in Canada/Australia/ Europe has been found to coincide with a fall in the number of road accidents.

Your body is on a 24-hour body-clock, which makes you wind down between 1 a.m. and 6 a.m. and again in the three hours directly after lunch. Siestas are recommended for good health.