When I covered how much you should sleep, you will recall that I categorized sleeping and wake-up times based on sleep cycles. I advised you to sleep at least five or six sleep cycles, amounting to 7.5 or 9 hours of sleep with a 15-minute allowance to fall asleep. If you have not read the article, you can read it here. It is a nice prerequisite to understanding the stages of sleep.

So, what are sleep cycles? These are the stages of sleep you go through each time you go to bed. Successfully moving through each stage ensures that you wake up feeling rested enough. Back in the day, people categorized sleep stages into 5. However, this has since changed, and we now recognize 4 stages of sleep. One of these is a rapid eye movement stage (REM), while the other three are non-REM (NREM). This academic resource sums it all, but I will break it down further to help you understand how you sleep.

The 4 Stages of Sleep

NREM Stage 1 (5-10 minutes)

As you go to sleep, you may have noticed that you do not fall asleep immediately. Instead, you remain in a bit of limbo, coming in and out of sleep. You may even respond to external sounds at this point as your brain activity and breathing slow. You even feel relaxed, and for some people, a twitch here and there ensues. It is easy for someone to wake you at this stage.

NREM Stage 2 (10-60 minutes per cycle)

Did you know? Most people spend half their sleep time at this stage. When you successfully get to this stage, your eye movements stop, your breathing becomes regular, and your temperature falls. Moreover, you become less responsive to external sounds, and anyone trying to wake you must put in some effort. Finally, as you fall deeper into sleep, your brain starts filtering memories from the previous day in preparation for the third stage.

This stage averages 20 minutes for most people. The first stage is usually short, but as you fall deeper into sleep and cycle through the stages, stage 2 becomes longer. You probably spend half of your total sleep time in this stage.

NREM Stage 3 (20-40 minutes)

At this point, someone cooking in the next room would barely wake you up. Your muscles relax completely, your breathing slows down, and your blood pressure suffers a drop. Sooner than you know it, you fall into a deep sleep. This stage allows your body to start physical repair work. Additionally, your brain collects memories, e.g., facts and experiences with other people. So, you can see that not sleeping enough can deter you from passing a paper you have studied for in the last two weeks. After all, the brain would barely have the time to consolidate this information for future use.

Our bodies spend a lot of time on this stage during the first hours of sleep. However, during the second half of the sleep cycle, we spend less time on this stage and more on stage 2 and the REM stage.

REM Sleep (10-60 minutes)

This stage features immobilization of voluntary muscles and brain awareness that you are about to wake up. Your eyes and breathing muscles work as usual, but if you were to wake up at this stage, you would not be able to turn, which can be scary. The REM owes to the rapid movement of the eyes. While you may be completely asleep, anyone looking at you can see your eyes moving fast, indicating that you are now experiencing a vivid dream. However, because your muscles are immobilized, you cannot act out your dreams, which is good. Moreover, this stage also allows the brain to cement memories and process emotional experiences.

Most people get to this stage after having been asleep for at least 90 minutes. As the night progresses, this stage becomes longer. For most adults, this stage accounts for about 25% of their total sleep time.

Are the stages of sleep successive?

You might think that the stages of sleep follow each other based on the breakdown above, but this is not the case. For example, suppose you sleep soundly and do not get interrupted, your stages of sleep would be as follows:

• NREM Stage 1
• NREM Stage 2
• NREM Stage 3
• NREM Stage 2
• REM Sleep

That would be your complete sleep cycle. You would then go back to:

• NREM Stage 2
• NREM Stage 3
• NREM Stage 2
• REM Sleep

The sleep cycle keeps going like this until you finally wake up. Then, stage 2 gradually lengthens while stage 3 becomes shorter as you sleep. So, how much sleep should you get each night with sleep cycles considered?

Here is how much you should sleep each night, with all factors considered.