how many sleep cycles do we have a night
The average cycle is 1 hour and 30 minutes, however cycle length can vary from 60-120 mins. depending on the person. If we truly were to sleep without any disturbances and no alarm clocks, we would always wake up on a multiple of 90 minutes. For example after: 4.5 hours, 6 hours, or 9 hours of sleep. E.g., 5 complete sleep cycles = 90 mins + 90 mins. + 90 mins. + 90 mins + 90 mins = 7.5 hours of sleep.