Sleep is not a uniform process. Instead, our bodies cycle through four (or four, discounting N-REM 4) discrete stages. We experience these sleep cycles several times throughout the night - typically between four and six times.
Each sleep stage is vital for restorative sleep, contributing to the physical repair of our bodies, the stabilization of our emotional state, the acuity of our mental faculties, and more.
Your brain is erupting in these incredible bursts of electrical activity going through all of these fantastic sleep stages. It's an electrical ballet that takes place at night.
Dr. Matthew Walker,
Many people mistake restorative sleep for a specific phase of sleep, such as deep sleep. This misunderstanding leads them on a path of faux optimization. In fact, over-optimizing for one or more sleep stages may drive detrimental outcomes, not improvement.
All five sleep stages are important, with each playing a specific role in restorative sleep. It’s only by taking a holistic view of sleep quality that we can unlock the full potential of natural sleep.
During Rapid Eye Movement (REM) sleep, our brain activity spikes and we can experience vivid dreams. Our bodies are active, too. Our eyes flick back and forth, our heart rates increase, and our breathing quickens. This sleep stage is mentally and emotionally restorative. It allows the mind to cleanse negative experiences and absorb fresh information. Long-term deficiency in REM sleep may be linked to depression, anxiety, and other mood disorders.
More: What is REM Sleep?
Non-REM stages one and two, jointly known as light sleep, account for 60% of our nightly sleep. It’s the generalist phase, contributing to a gamut of functions, including memory, body repair, and hormone regulation, to name a few. Few - if any - adults suffer from too little light sleep. More commonly, an excess of light sleep is due to the suppression of deep sleep or REM sleep.
As sleep deepens, we enter non-REM stages three and four, jointly called deep sleep. This sleep stage rehabilitates the body and reverses physical exhaustion. It replenishes energy, repairs muscles, and buoys the immune system. Insufficient deep sleep weakens immunity and slows recovery, often leading to reduced physical performance or even illness.
Although the sleep cycle repeats itself, its pattern varies through the night. Most REM sleep, for example, occurs during the latter half of the night. Improving the quality of our sleep requires us to recognize these nuances and safeguard sufficient sleeping time for us to reach later stages.
So too must we align our sleep to our natural biological rhythms and brain function. Morning larks working into the night and night owls rising at the dawn are fighting a losing battle - and compromising their sleep in the process.
I can't just dial up my deep sleep by an hour and a half or reduce my REM sleep down a little bit. You have to let sleep unfold naturally.
Dr. Matthew Walker,
Sleep is your superpower
Improving the composition and quality of sleep rests on three pillars: duration, efficiency, and stages.
The first concern is getting enough total sleep. sleeping for long enough, you create enough opportunity for REM sleep.
Fragmented sleep is not restorative sleep. By improving sleep efficiency, you ensure you reach later stages like REM.
All stages of sleep are important and all have a purpose. We should strive for an optimal balance of all 5 sleep stages.