It was like a thief in the night. At first I battled to fall asleep, so a few hours were lopped off my usual eight. This wasn't too bad because I could find something to keep me busy until my brain felt tired enough to shut down,' says Tracey, a 30-something journalist.

'It got more troublesome when the alarm clock in my head went off every morning at 3am or 4am.

Most people have experienced some sleeplessness at one time or another. About 30-40% of adults indicate some level of insomnia within a year, and 10-15% indicate that insomnia is chronic and/or severe, says Dr Irshaad Ebrahim, specialist neuropsychiatrist in sleep disorders at the London Sleep Centre (Harley Street, UK) and The Constantia Sleep Centre (SA).

When we talk about getting 'enough sleep', we consider the quantity of sleep required, thought to be between seven and eight hours a night, says Dr Ebrahim. But, he says, 'it's the quality of sleep that's probably more important'.

So what counts as quality sleep?

Sleep is divided into five cycles, stages 1 to 4, or non-REM sleep, followed by REM sleep. Stages 1 and 2 are light enough for us to be woken up by a knock on the door.

Stages 3 and 4 are considered deep or slow-wave sleep, and are essential to waking up feeling like we've had a good rest.

But to get to REM, the last stage, you have to go through the full cycle of non-REM. If you're interrupted at any stage, by a poke in the ribs, for example, the cycle loops back to Stage 1. If you're feeling wiped out in the morning, chances are you haven't had enough or haven't had a chance to get to Stages 3 and 4.

Too little REM and your mind starts to play tricks on you.

In That Memory Book, Cathryn Jakobson Ramin describes slow-wave sleep as a time when the brain extracts meaning from the information that comes at it during the day. 'Because the brain is able to run through events that occurred during the day and look for interesting juxtapositions, slow-wave sleep enhances creativity,' she says.

'REM sleep is the cleanup crew, brought in to sweep up the detritus after slow-wave has finished its gig. In REM sleep, the brain examines the just-processed material, deciding what to keep and what to toss. If there's been little or no slow-wave sleep, the cleaners can make a bad mistake, carting tomorrow's carefully prepared speech off in a dustbin.'

Top five sleep-easy tips

Go to bed only when you think you can fall asleep.
If you haven't fallen asleep within 20 minutes, get up and do something else until you feel tired.

Wind down in the evening.
Rather than watching television, take a relaxing bath.

Avoid caffeine, nicotine, sugar and alcohol before bedtime.
if you want a snack, eat protein and not carbohydrates. >p>Don't nap during the day.
According to Marlene Gounder at the Sleep Clinic, Life Vincent Pallotti hospital, no adult should nap in the day unless they had a bad night.

Get regular exercise.
Yoga is particularly good for relaxation.