– Stage 2: light sleep,

– Stages 3 and 4: deep slow-wave sleep,

– Stage 5, Rapid Eye Movement (REM) sleep. 

 
 Minutes
 Percentage
 
Wake time
 12
 3%
 
Stage 1
 48
 12%
 
Stage 2
 159
 39%
 
Stages 3 and 4
 117
 28%
 
Stage 5
 76
 18%
 
Total
 412
 100%
 

Sleep composition and organization (Benoit, 1984)
 

 
 
After sleep onset, the subject progresses through Stages 2, 3 and 4. He remains for a certain time at Stage 4, whereafter sleep becomes lighter with a return to Stage 2 which leads to the first REM phase. This terminates the first sleep cycle.
 
A normal night's sleep includes 4 to 5 cycles depending on total sleep time. The REM stage occurs every 90 to 120 minutes.
 
Deep slow-wave sleep (Stages 3 and 4) occurs mainly in the first half of the night.
 
The REM sleep episodes are longer during the second half of the night.
6.5.1.2. SPONTANEOUS VARIATIONS BETWEEN INDIVIDUALS

6.5.1.2.1. Sleep time: short & long sleepers 

Average sleep time is between 7 and 8 hours.
It is accepted that the minimum and maximum sleep time limits are 4 hours and 11 hours respectively.
Sleep times of less than 5 . hours are recorded with short sleepers. Long sleepers sleep for more than 9 . hours.
Short and long sleepers represent less than 5% of the total population.
The difference between short and long sleepers is mainly explained by the differences in Stage 2 and REM sleep.
Long sleepers have more awakenings, more light sleep and more REM sleep stages but almost the same amount of deep slow-wave sleep (Stages 3 and 4) as short sleepers.
 

 
6.5.1.2.2. Spontaneous sleep times: morningness –eveningness 

The body temperature cycle is an excellent biological clock phase marker. It is said to be normal when the thermal minimum is around 5am, in advance when it occurs before, and delayed when it occurs after 5am.
 
Evening types have a biological clock phase, which is delayed with regard to the environmental synchronizers, and morning types have a biological clock phase, which is in advance of the environmental synchronizers.
 
Spontaneous sleep onset and wake onset are related to the biological clock phase. Advance in phase leads to early bedtimes and early rising. A delay in the biological clock leads to the opposite phenomenon.
 
Sleep onset times correspond, on average, to 10pm and 1am for morning types and evening types respectively.
　
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