How Long Is One Sleep Cycle And What Is Actually Happening

We spend one third of our lives sleeping. It's one of the few activities we continually do throughout our lives. Whether we are young or old, sleep is vital to our way of life and health. But how much do we actually know about sleep? We mostly take it for granted and never actually learn what's happening while we sleep. The fact is, a lot is going on while we sleep. Today we answer the question: how long is one sleep cycle, and we look a little further into what is going on during these cycles.

how long is one sleep cycle

You may also be interested in:

How Long Is Each Sleep Cycle?

The length of each sleep cycle will vary from person to person and changes with age. For our purposes we can say that a typical sleep cycle for an average healthy adult lasts for approximately 90 minutes. Interestingly the first sleep cycle we go through during a normal night's sleep will last for around 120 minutes, and as the night progresses they will decrease in time and average at 90 mins.

What Happens During A Sleep Cycle?

sleep cycles

Each sleep cycle is further divided into different phases of sleep which have their own unique characteristics. 

Each sleep cycle begins with what is known as non-rapid-eye-movement sleep (or non-REM)​. This phase is itself made up of three different stages: N1, N2 and N3. As we progress from N1 to N2 to N3, our sleep becomes increasingly deep. In fact as we go through this progression, we become increasingly unresponsive and more difficult to awaken. 

This deep sleep cycle is typically broken down into the following time intervals:

N1: 1-7minutes

N2: 10-25 minutes

N3: 20-40 minutes​

​After the deep N3 stage we breifly go back to N2 before entering the rapid-eye-movement (or REM) sleep phase.

Did you know: our arms and legs are paralyzed during REM sleep so that we don't act out our dreams (Harvard Medical School)

If you have ever watched someone sleeping (not in a creepy way!) you may have noticed their eyes flickering. This is what REM sleep looks like, and it is the active part of sleep which is associated with dreaming. 

If you wake up during REM sleep you are much more likely to remember your dreams than if you wake up during non-REM sleep. According to the ​Division of Sleep Medicine at the Harvard Medical School, people who are woken during REM sleep often report having strange and vivid dreams. REM sleep cycle time makes up approximately 20-25% of our sleep.

The deep sleep light sleep cycle continues throughout the night with short periods of pseudo-sleep occurring between sleep cycles. As the night progresses the make up of the sleep cycles does however change. At the earlier stages we spend a heavier amount in non-REM sleep and less in REM sleep. However as the night progresses we spend increasingly amounts of each sleep cycle in REM and less in non-REM.

How long is one sleep cycle? Now you know.

We hope this answers your question, how long is one sleep cycle. If you have something to share, please leave a comment below.