What happens to your body while you're asleep We spend about one-third of our lives asleep. But far from being wasted time, from the moment we slide into unconsciousness, a whole raft of functions takes place to make sure that we get optimal benefit from our nightly rest. Sleep is the time the body can undergo repair and detoxification. Poor sleep patterns are linked to poor health - and those who sleep less than six hours a night have a shorter life expectancy than those who sleep for longer. So sleep has a profound effect on our mental, emotional and physical wellbeing. Here, Daily Mail writer Angela Epstein explains how the body works on when we drift off. The brain Sleep may seem to be a passive and dormant state, but even though activity in the cortex - the surface of the brain - drops by about 40 per cent while we are in the first phases of sleep, the brain remains highly active during later stages of the night. A typical night's sleep comprises five different sleep cycles, each lasting about 90 minutes. The first four stages of each cycle are regarded as quiet sleep or non-rapid eye move-ment (NREM). The final stage is denoted by rapid eye movement (REM). During the first stage of sleep, brain waves are small undulations. During stage two these intersperse with electrical signals called sleep spindles - small bursts of activity lasting a couple of seconds which keep us in a state of