10 interesting facts about sleep - Other than "Im sleepy"

1. The record for the longest period without sleep is 18 days, 21 hours, 40 minutes during a rocking chair marathon. The record holder reported hallucinations, paranoia, blurred vision, slurred speech and memory and concentration lapses.

2. It’s impossible to tell if someone is really awake without close medical supervision. People can take cat naps with their eyes open without even being aware of it.

3. Anything less than five minutes to fall asleep at night means you’re sleep deprived. The ideal is between 10 and 15 minutes, meaning you’re still tired enough to sleep deeply, but not so exhausted you feel sleepy by day.

4. Dreams, once thought to occur only during REM (Rapid Eye Movement) sleep, also occur (but to a lesser extent) in non-REM sleep phases. It’s possible there may not be a single moment of our sleep when we are actually dreamless.

5. 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.

6. Certain types of eye movements during REM sleep correspond to specific movements in dreams, suggesting at least part of the dreaming process is analagous to watching a film

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

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

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

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