The average Briton gets six-and-a-half hours' sleep a night, according to the Sleep Council. Katharina Wulff of the Nuffield Department of Clinical Neurosciences showed BBC journalist Michael Mosley what happens when we sleep.
In the Sleep Centre at the John Radcliffe Hospital she fitted him up with a portable electro-encephalograph to measure brain wave activity. He slept for seven and a half hours and discussed the results with Katharina the next day, who explained the difference between deep sleep and REM (rapid eye movement) sleep. We get more REM sleep in the last half of the night, when our brains process the day's experiences. This means that if we are woken up unexpectedly, our brains may not have had time to process particularly emotional events.
Michael Mosley talked to Katharina as part of his investigation of an unusual experiment with seven volunteers designed to find out how much an extra hour's sleep might change us.