This article is part of a series regarding the ‘basics’ you should know about your sleep. You can find the table of contents of this series here.

‍

Age is a crucial factor; an elderly person will not have the same sleep architecture as a child neither as an adult.

In addition to this, sleep patterns can be affected by many factors including the amount of recent sleep or wakefulness, the time schedule of sleep, an individual’s internal clock, behaviors prior to sleep such as exercise, eating, stress or environmental conditions such as temperature, light, and various chemicals of the body.

And there's more to it than that! The amount of time we spend in a particular stage of sleep will shift over the course of the night (we will talk about this later). 

As a matter of fact, we won’t be describing the duration of the different phases in time but rather in proportion to the total sleep.

REMEMBER, THIS IS JUST A RUDE EXAMPLE OF WHAT YOUR CYCLES MAY LOOK LIKE.

That being said, we can try to visualize the path that sleep takes for a healthy adult in its first cycle. 

• When you start sleeping, you will shift from wakefulness to N1, the first stage of light sleep. This is a very special time that a good number of people manage to identify since many people experience sudden muscle contractions or a sensation of falling. If someone wakes you up during N1, you will say that you did not even start sleeping. This first period of N1 typically corresponds to 5% of total sleep.
  

• The second stage of light sleep, or N2, comes next and generally corresponds to 40% of total sleep. That’s the sleep stage in which you spend the majority of your time as an adult.
  

• As N2 sleep progresses, there is a gradual shift to N3, the third stage of NREM sleep but the first stage of deep sleep. This stage generally corresponds to 5% of total sleep.

From now on, you become less responsive to external stimuli, and it becomes very difficult to wake up an individual from sleep.

• This is where you enter in the N4 stage, the very deep sleep that corresponds to 15-20% of total sleep.
  

• Following the N4 stage of sleep, a series of body movements usually signals a shift to the REM stage with a return to lighter sleep stages. Typically, a 5% period of N3 and N2 precedes the initial REM sleep episode. 
  

• Then you enter in your first REM stage that corresponds to 20-25% of total sleep.

For the remaining time, there is a transition phase following REM where we often wake up without remembering before starting a new cycle.

And so on. The cycles follow one another.

But as we said earlier, the amount of time we spend in a particular sleep stage starts to shift over the course of the night. In fact, during the final 4th, 5th and 6th sleep cycles of your sleep, the time spent in deep sleep drastically lowers (N4 is even deleted) to allocate additional time to REM sleep and light sleep. That’s why there’s a good chance that you wake up after a dream in the morning if you sleep enough.

The same reduction in deep sleep is happening as we move from childhood to adulthood and from adulthood to elderhood. In addition to losing our deep sleep, we also cut back on REM sleep as we age.

‍

‍

To summarize, the architecture of your sleep can look like: 

At the beginning of your sleep

Awake – N1 (light sleep) – N2 (light sleep) – N3 (deep sleep) – N4 (deep sleep) – N3 (deep sleep) – N2 (light sleep) – N5 (REM Sleep)

‍

At the end of your sleep

N1 (light sleep) – N2 (light sleep) – N1(light sleep) – N5 (REM Sleep) – Awake

Conclusion

You are now probably wondering how much total sleep should you get? That’s what we are going to discuss in the final episode of the series: How much sleep should I get? Sleep demystified. Basics n°5 about sleep