SLEEP
The sleep cycle refers to the sequence of stages during sleep according to research on the subject. A healthy person has four to seven sleep cycles of about 70 to 110 minutes every night, in which the NREM stages N1, N2 and N3 and again N2 are followed by REM sleep. In the following cycles, the proportion of deep sleep decreases and disappears completely in the later cycles; whereas the REM part increases towards the end of sleep period. read more ...