You hit the lights, close your eyes, and boom — just like that, eight hours of your life goes by in the wink of an eye. But in real time it’s not that simple. While we doze, our brain undergoes intense activity as it passes from stage to stage and cycle to cycle. At times, our brain is actually more active while we sleep than when we’re awake.
So why should you care about the science behind snoozing? Understanding your sleep cycles allows you to refine and perfect your rest. It’s part of being sleep-conscious.
Here’s exactly what happens during each sleep cycle — and why it matters for your tomorrow.
Sleep Cycle Stages
Each night, your brain goes through a series of five stages that make up a sleep cycle.
Stage 1 (NREM)
This is the first phase of light sleep, when your brain and body are in limbo between wakefulness and sleep for about 10 minutes. You may hear sounds and conversations around you, but feel unwilling to respond.
During this stage, your breathing and heartbeat begin to slow as your muscle tension and core body temperature decrease. People often experience a falling sensation and twitches in Stage 1 known as hypnic (hypnagogic) jerks.
Stage 2 (NREM)
Next, your consciousness of the outside world fades as your body prepares itself for deep sleep. This lasts for about 20 minutes of the sleep cycle and accounts for roughly 50 percent of total sleep.
In Stage 2, you become increasingly relaxed as your eye movement stops, your heartrate slows, and your body temperature decreases. Bursts of electrical activity known as sleep spindles help maintain your brain’s communication system, improve your memory formation, and boost your intellectual ability.
Stage 3 and 4 (NREM)
As you fall into deep sleep, you’re cut off from the outside world, unaware of outside stimuli. Stages 3 and 4 — which account for about 20 percent of total sleep — are the most difficult stages to wake up from, and if you do wake suddenly, you’ll feel disoriented.
While in deep sleep, your blood pressure falls, your breathing slows, and your body temperature drops even lower. This is the restorative phase of sleep; your body repairs tissue and strengthens your immune system.
Stage 5 (REM)
Rapid eye movement, or REM, begins as your body is physically paralyzed, but your brain is bursting with activity. This is when dreams occur. Stage 5 only lasts about ten minutes in the first cycle, but it can last as long as an hour in the final one.
During REM sleep, your heart rate increases, your blood pressure rises, and your breathing becomes irregular. This stage helps you process memories and emotions that are crucial for learning.
You typically experience three or four sleep cycles per night, which last between 45 to 90 minutes in length. Here’s how they differ:
- Cycle One: A short period of light sleep, followed by a long period of deep sleep, and a brief period of REM.
- Cycle Two: Light sleep and REM increase, deep sleep decreases.
- Cycle Three & Four: Light sleep and REM continue to increase, deep sleep tapers further.
How to Optimize Your Sleep Cycles
Keep a Consistent Schedule
Stick to the same bedtime and wake time every day — including on the weekends. Keeping a consistent sleep schedule helps you regulate your body clock so you can fall asleep quicker and wake up easier.
Skip the Snooze
Once your body becomes familiar with a routine, it’ll prepare itself to wake up during the lighter stages of sleep. But the snooze button turns this process on its head. Those extra zzz’s will leave you feeling more tired if the second alarm wakes you during deep sleep.
Stay on Track
Sleep trackers monitor movement using actigraphs to estimate total sleep time and after-sleep waking. By receiving personalized insights, you can analyze your overall sleep performance and adjust your schedule accordingly. Some sleep trackers even track your sleep patterns in order to wake you up during light sleep.