Like many biological functions, sleep is both unique to each person and follows predictable patterns. The concept of REM and sleep cycles are generally familiar, but most people don’t actually understand how the sleep cycle works or why their sleep habits form the way they do. These cycles relate primarily to the depth of sleep and when you dream, and repeat about every one to three hours. This can explain why you might wake up after three hours of sleep feeling energized and ready to go, but four hours, while longer, leaves you groggy and feeling profoundly under-rested. Asking anyone what they think the deepest stage of sleep is, they are likely to answer “REM dreaming”, however, dreaming is, in fact, one of the lightest stages of sleep. You get your best rest during what is referred to as slow wave sleep.
Sleep by The Numbers
The stages of sleep are broken up into four stages, which refer to the depth of slumber and how easy it is to wake up from each stage. According to the Center for Sound Sleep, stage one is initiated as you begin to nod off. Whether at the end of your work day or with your head on the pillow, your body is telling you it is ready to sleep and would willingly do so if you would only hold still.
In stage two, your breathing slows down and your thoughts drift, but you are not fully down yet. In this stage, if the phone rings or your child needs a glass of water, you are up quickly without grogginess, able to handle another few hours awake without hassle.
Stages 3 & 4 – Slow Wave
If nothing interrupts you in stage two, stage three begins and so too does slow-wave sleep. This is the sleep it’s hard to leave, and waking feels like pulling yourself up through molasses. Slow-wave sleep continues through to stage four in which you ‘sleep like the dead’ and may need to be shaken to wake up.
Finally, before REM can begin, you actually rise back up into stage two and your brain spends some time sorting through your conscious and subconscious thoughts. This is why it’s really pretty easy to wake up from a dream, but not from deep, dreamless sleep. When you’re done with the first round of REM, your sleep begins to deepen again and the cycle restarts.
Why Is It Called ‘Slow Wave’ Sleep?
You may wonder, if REM is the special important phase, why does the body even bother with slow wave deep sleep? Each phase is important in its own way. As you enter the deepest part of sleep, your brain emits “larger amounts of slow-wave EEG (brainwave activity) than in other stages” according to Harvard Med. These slow waves are known as delta activity. While you are in this stage, your body uses minimal resources for activity, allowing it to repurpose those resources for other important tasks like “regenerating tissues, building bones and muscle, recharging energy stores and strengthening the immune system” as reported by the Nutrition Review.
Many of the health benefits attributed to sleep as a whole, in fact, come from the slow-wave stage, without which you would feel tired and un-energized after waking even if you had good dreams. Some people have a hard time reaching the deeper stages of sleep and may need to take extra effort to relax before bed. Want to make use of this information? Don’t nap for more than 30 minutes in a public place, take a long bath before bed, and try setting your alarm to wake you during one of the lighter phases of sleep to avoid that sluggish groggy morning feeling.