Your brain goes through numerous sleep cycles each night. Each cycle begins with light sleep, proceeds to deep sleep dreams, and finally returns to the light. Each cycle lasts around 90 minutes. The 90-minute snooze rule is predicated on waking up at the end of a sleep cycle, which includes 90 minutes of healthy REM sleep. We feel exhausted, tired, and grumpy when we wake up in the middle of a deep sleep since we believe we did not receive enough sleep. For example, If you need to get up at 6 a.m., go to bed around 9 p.m. to receive nine hours of sleep and six sleep cycles, or 10:30 p.m. to get seven and a half hours of sleep and five sleep cycles.