Whether measured in a sleep lab or with a wearable device, a recorded night of sleep will be broken down into four unique sleep "stages": Awake, Light, Deep/Slow Wave Sleep (SWS) Sleep and Rapid Eye Movement (REM). The average adult will cycle through these stages 3-5 times per night.
The sleep stage "Awake" is as simple as it sounds. This is the time measured during the night where you are not fully asleep. It is entirely normal for someone to spend upwards of 30 minutes to 1 hour awake during the night, even if there is no memory of the time spent awake. The periods of 1-3 minutes spent awake are quite common and rarely is an individual conscious for all, if any, of those awake periods.
This stage is the transition period between "awake" and "deep" sleep, when your body is still partially responsive to the environment but also partially attuned to the restoration that takes place in deep sleep, such as muscle recovery. Your breathing will slow and your body temperature will drop slightly. A healthy amount of light sleep is around 50% of your total sleep time.
Deep Sleep / SWS (Slow Wave Sleep)
When your body enters deep sleep, this is a crucial time for your muscles to repair and rebuild. This is also the time when your immune system is fortified. Your breathing and heart rate are at their slowest as your body fully relaxes. Your brain activity involves delta waves, which is why this stage is often called slow wave sleep. A healthy amount of time spent in deep sleep is 20-25% of your total sleep time.
REM (Rapid Eye Movement)
During REM, not only the body but the brain is restored. While your body is entirely still with the exception of your eyes (which is how REM gets its name), your brain is actually the most active. This stage of the sleep process involves dreaming, and also the cementing of activities and acquired knowledge as memories. Like deep sleep, healthy amount of time spent in REM is 20-25% of your total sleep time.
Make the most of your sleep
Sleep deprivation negatively affects health in a myriad of ways. By tracking your sleep patterns with your COROS watch, you can see what changes need to be made to recover better and feel more restored when you start each day. You have probably heard that the average adult needs 7-9 hours of sleep per night. However, it's important to keep in mind that the quality of sleep matters just as much as the quantity. A truly restorative sleep is one where you cycle through the four stages smoothly, with as little wake time as possible, about 3 to 5 times.
Reaching deep sleep and REM is crucial for proper recovery and rehabilitating your muscles and brain. There are also some concrete steps that you can take to improve your sleep quality, such as avoiding screens and alcohol before going to bed, getting sufficient daylight while awake, and sticking to a consistent sleep schedule.
For information on how COROS watches track your sleep, please see this article.