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The secret world of sleep

We all know that lack of sleep leads to forgetfulness, but the exact effect it has on cognitive function is quite alarming. Seventeen hours of sustained wakefulness is said to cause the equivalent effect on performance as two glasses of wine.

Contrary to popular belief, deep sleep is not achieved in the REM (rapid eye movement) phase, of which we have three to five periods a night. Experts say we have our deepest sleep in a phase known as 'slow-wave sleep'.

Ever wondered why you tend to wake up just before the alarm clock goes off? According to researchers, the body has a subconscious alarm clock which enables some people to wake up when they want to. The unconscious anticipation of rising triggers a burst of the stress hormone, adrenocorticotropin, which in turn wakes the sleeper.

Sleep is also important for healing, regeneration and growth. Studies show that hormone levels increase and changes in immune function occur during slow-wave sleep.

The record for the longest period without sleep is 18 days, 21 hours and 40 minutes. The record holder reported hallucinations, paranoia, slurred speech and concentration lapses.