All sleep stages in a row
You know that feeling? That the alarm goes off and you were just dreaming. Or that you were in a very deep sleep, so that the alarm signal seemed to come from very far. Apparently not all sleep is the same. You sleep in different phases and they are all unique.
Each night you go through different stages of sleep. One of them is REM sleep, the well-known dream sleep. However, most of it is non-REM sleep (NREM), the “normal” sleep. These sleep phases do not simply overlap. There is a fixed order. And you go through this whole list, the so-called sleep cycle, about four to six times a night. Below are the stages you sleep per sleep cycle.
Transition phase between wakefulness and sleep
The first sleep stage of NREM sleep is a transition phase between the waking and sleeping states. This stage only lasts three to five minutes. The body temperature drops and the muscles relax. Slow Eye Movements (SEM) can be seen during this stage. You probably know that feeling when you struggle with your sleep. Your eyes then slowly turn away and you have trouble keeping them open. In this phase you can often also feel a shock, sometimes with the feeling that you are falling. This is a sleep fit; a short contraction in the muscles of your arms or legs. This will keep you fully awake for a while. Sounds also wake you up easily in this phase.
Deeper sleep
The second stage of sleep is a little deeper and lasts about thirty to forty minutes. You sleep the most in this stage of sleep: up to 50 percent of the total sleep time per night. It is the beginning of ‘real’ sleep. You will no longer be woken up by just any noise at this stage.
Very deep sleep
Stages three and four are usually considered one whole. In this phase you are very relaxed and difficult to wake up. Your breathing is deep and your heartbeat is slow and regular. During the onset of the night, this phase lasts a very long time. But in the following cycles this phase lasts shorter and shorter. Growth hormones are released, your body recovers and gains new strength. As you get older, these deep sleep phases get shorter and shorter. You will therefore notice that sleeping is not nearly as refreshing as before.
REM sleep
After stage four, the stage of REM sleep or dream sleep begins. The large muscles of your limbs are then paralyzed. If not, you could jump out of bed and start pursuing your dreams. You can tell if someone is in REM sleep by the rapid eye movements under the closed eyelids. The brain is fully active during this phase. Scientists are not yet sure why the brain is so active. But it is suspected that it has to do with processing information. As the night progresses, the periods of REM sleep become longer and longer. In total, dream sleep takes up 20 to 25 percent of the sleep duration.