Overview of Sleep Stages

These are typical brainwaves in the different sleep stages!

When we sleep, our bodies cycle through three distinct phases. It wasn’t until the 1950s that scientists discovered these sleep stages. The sleep stages are Light sleep, Deep sleep, and REM (Rapid Eye Movement). Many people cycle through these stages in a distinct pattern, Light deep → Deep sleep → Light sleep → REM, but these cycles can vary. It’s common to bounce between Light sleep and REM as you sleep throughout the night.
In a healthy night of sleep, we cycle through the sleep stages four to five times. It’s common for your body to complete all of these stages in a 90-minute cycle, but this timing can vary. Sometimes our bodies cycle through each stage quickly, whereas other times we linger in certain sleep stages.

Light Sleep
We spend the majority of the night in Light sleep. Light sleep is similar to being awake in that we can talk, move, and regulate our body temperature while we are in Light sleep. We also dream, but our dreams in Light sleep aren’t the fully formed stories that we usually characterize as dreams. Instead, our Light sleep dreams are flashes of memories or images that usually don’t form any coherent narrative. Light Sleep is the closest sleep stage to being awake, and we are most easily awoken during this stage. If woken during Light sleep, you might not even have noticed that you were asleep. It is ideal to wake up during Light sleep, as you will be able to wake up much more easily and feel more alert than waking up in either of the other sleep stages.

Deep Sleep
Deep sleep is the most restorative stage in the sleep cycle. In this stage, our brainwaves become dramatically longer, and our daily experiences are turned into long-term memory. Deep sleep is vital to feeling rejuvenated and learning effectively; without deep sleep, it is difficult to effectively learn and process information. Deep sleep is vital, but it can be difficult to achieve. As we sleep, we spend less and less time in Deep sleep. In the beginning of the night, it is common to spend up to 50% of the first sleep cycle in Deep sleep. By the end of the night, we only spend around 2% of the sleep cycle in Deep sleep. As we age, our bodies tend to spend less time in Deep sleep per sleep cycle. This is why sleep can feel less rejuvenating the older we get, even if we sleep for the same amount of time.

In REM, like in Light sleep, our brainwaves are similar to when we are awake. Our dreams in REM often form stories that we remember in the morning, as opposed to the fleeting images or memories that characterize Light sleep dreams. During REM our bodies are actually paralyzed, meaning that we are completely motionless except for our eyes. If you see a sleeping person staying very still while their eyes move underneath their eyelids, they’re probably in REM. When we are in REM, our bodies lose thermoregulation, which means that our bodies cannot regulate our temperatures. In effect, our bodies behave like cold-blooded animals, since our bodies change temperature based on how hot or cold our sleep environment is.