Sleep Facts
Ducks can keep half of the brain awake while the other half sleeps

Sleep facts

sleeping baboons

Baboons sleep about 10 hours a night on average

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REM sleep occurs in bursts totalling about 2 hours a night, usually beginning about 90 minutes after falling asleep.

Dreams, once thought to occur only during REM sleep, also occur (but to a lesser extent) in non-REM sleep phases.

►  REM dreams are characterised by bizarre plots, but non-REM dreams are repetitive and thought-like, with little imagery - obsessively returning to a suspicion you left your mobile phone somewhere, for example.

Elephants sleep standing up during non-REM sleep, but lie down for REM sleep.

► Some scientists believe we dream to fix experiences in long-term memory, that is, we dream about things worth remembering. Others reckon we dream about things worth forgetting - to eliminate overlapping memories that would otherwise clog up our brains.

 Dreams may not serve any purpose at all but be merely a meaningless byproduct of two evolutionary adaptations - sleep and consciousness.

REM sleep may help developing brains mature. Premature babies have 75 per cent REM sleep, 10 per cent more than full-term bubs. Similarly, a newborn kitten puppy rat or hampster experiences only REM sleep, while a newborn guinea pig (which is much more developed at birth) has almost no REM sleep at all.

Scientists have not been able to replicate a 1998 study showing a bright light shone on the backs of human knees can reset the brain's sleep-wake clock.

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 role.

The NRMA estimates fatigue is involved in one in 6 fatal road accidents.

The "natural alarm clock" which enables some people to wake up more or less when they want to is caused by a burst of the stress hormone adrenocorticotropin, according to research. Researchers say this reflects an unconscious anticipation of the stress of waking up.

Tiny luminous rays from a digital alarm clock can be enough to disrupt the sleep cycle even if you do not fully wake. The light turns off a "neural switch" in the brain, causing levels of a key sleep chemical to decline within minutes.

To drop off we must cool off; body temperature and the brain's sleep-wake cycle are closely linked. That's why hot summer nights can cause a restless sleep. The blood flow mechanism that transfers core body heat to the skin works best between 18 and 30 degrees. But later in life, the comfort zone shrinks to between 23 and 25 degrees - one reason why older people may get less sleep

A night on the grog will help you get to sleep but it will not be of good quality and will reduce the amount of REM or dreaming sleep

After five nights of partial sleep deprivation, three drinks will have the same effect on your body as six would when you've slept enough.

Humans sleep on average around three hours less than other primates like chimps, rhesus monkeys, squirrel monkeys and baboons, all of whom sleep for 10 hours.

Ducks at risk of attack by predators are able to balance the need for sleep and survival, keeping one half of the brain awake while the other slips into sleep mode.

Ten per cent of snorers have sleep apnoea, a disorder which causes sufferers to stop breathing up to 300 times a night and increases the risk of suffering a heart attack or stroke.

Feeling tired can dangerously feel normal after a short time. Those deliberately deprived of sleep for research initially noticed greatly the effects on their alertness, mood and physical performance, but the awareness dropped off after the first few days.

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.

Most of what we know about sleep we've learned in the past 25 years.

As a group, 18 to 24 year-olds deprived of sleep suffer more from impaired performance than older adults.

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

The longest, scientifically-documented period without sleep is 11 days and is held by Randy Gardner, a 17 year old American. His health and behaviour was monitored and he experienced moodiness, problems with concentration, paranoia and hallucinations. However, he was still able to speak without slurring at a press conference on the eleventh day!