AP PSYCHOLOGY

Detailed explanation-1: -A full sleep cycle takes about 90 to 110 minutes. Your first REM period is short. As the night goes on, you’ll have longer REM sleep and less deep sleep.

Detailed explanation-2: -An average sleep cycle lasts about 90 minutes. Ideally, you need four to six cycles of sleep every 24 hours to feel fresh and rested. Each cycle contains four individual stages: three that form non-rapid eye movement (NREM) sleep and one rapid eye movement (REM) sleep.

Detailed explanation-3: -Sleep cycles across the night are only approximately 90 minutes in length. There are lots of individual differences in cycle length and the variation may be from around 60 to 110 minutes.

Detailed explanation-4: -For our purposes, it suffices to say that one sleep cycle lasts an average of 90 minutes: 65 minutes of normal, or non-REM (rapid eye movement), sleep; 20 minutes of REM sleep (in which we dream); and a final 5 minutes of non-REM sleep.

Detailed explanation-5: -The 90-minute snooze rule is based on timing the bedtime in a way that we wake up at the end of a sleep cycle-which has 90 minutes of proper REM sleep. When you wake up in the middle of a deep sleep, we end up feeling exhausted, tired and grumpy-because we feel we did not get proper sleep.