It might happen to us every night - and maybe sometimes more often - but it's still a deeply mysterious process.

An international group of researchers at the University of Cambridge is trying to find out what really happens in that drowsy twilight zone as we make the transition from waking to sleeping.

They are measuring, analysing and trying to understand how the conscious, controlled, waking person turns into an unaware, dreaming, sleeper.

They also want to know if this really is one of the most creative moments of the day.

Even though neuroscientists have carried out a huge amount of research on brain activity during sleep, the researchers at Cambridge say much less is known about the moments just before we enter sleep.

"Some people fall asleep very quickly, others take a long, long time," says Sridhar Rajan Jagannathan, a researcher from Chennai (Madras) in India, who has the unusual task of watching people fall asleep for a living.

Risk of accidents

This "transition" usually lasts between five and 20 minutes, says Mr Jagannathan, one of Cambridge's Gates Scholars, funded by a foundation set up by the US tech billionaire, Bill Gates.

But the behaviour within this time can be very different. For some, going into sleep is a smooth, uninterrupted descent. But others have more turbulence in the journey.