How Sleep Cycles Work


For many of us, sleep is not something we completely understand. Sure, we know that we need it every night. And we know that if we don’t get enough, we’ll have to load up on caffeine, and don’t even think about getting in our way. We also know that if we are woken up in the middle of a deep sleep, we feel confused, groggy and out of sorts.

Scientists are forever trying to understand the mechanics of exactly how and why we sleep. And while the heart of the matter remains somewhat mysterious, they have discovered plenty in their studies.

One aspect of sleep that is well understood is the sleep cycle. And it’s far more interesting that you might have thought!

You’ve probably heard that there are several components that make up a full sleep cycle. In fact, there are five distinct phases that occur from start to finish, and the time to complete one full cycle is approximately 90 minutes.

Here are the five stages of a full sleep cycle (and approximately how long each occurs):

Stage 1 (4-5%)

Light sleep
Muscles begin to relax (you may experience twitching)
Easy to rouse out of

Stage 2 (44-55%)

Non-REM (rapid eye movement)
Breathing and heart rate slow
Body temperature lowers slightly

Stage 3 (4-6%)

Deeper sleep begins, though still non-REM sleep
Brain begins to produce slower Delta waves

Stage 4 (12-15%)

Deepest non-REM sleep stage
Rhythmic breathing
Delta waves
Difficult to awaken

Stage 5 (20-25%)

REM sleep occurs
Heart rate speeds up
Breathing is rapid and shallow
Dreaming occurs

Studies have shown that people feel most rested after a full cycle is complete, in a 90 minute interval. For example, a person will feel better waking up after 4.5 hours rather than 5.5 hours.

One of the little know yet fascinating findings of sleep research has found that several centuries ago, people slept in two separate parts throughout the night. Each session was about 4 hours (possibly closer to four and a half), and was separated by a waking period of an hour or two.

In other words, the eight-hour sleep is a relatively new concept in our lives. And in fact, a body might naturally return to this pattern if given the chance. In the early 1900s, a scientist experimented on a group of people, keeping them in the dark for 14 hours each day. It didn’t take long for the participants to fall into a similar pattern – a four-hour sleep, followed by a 1-2-hour period of wakefulness, followed again by a second four-hour sleep.

Researchers have found evidence of the “first sleep” and the “second sleep” in literature of yore from across the globe. Today, however, we train ourselves to sleep around eight hours straight through. Perhaps it’s time we ask ourselves if we’re doing it right? Besides, wouldn’t it be fun to have a couple of hours in the middle of the night to contemplate life or read or… the possibilities are endless!

In our fast paced world, many people sacrifice sleep in order to squeeze more into each day. We do this in spite of the mountains of evidence that sleep is needed in order to maintain good physical and emotional health. We still don’t know everything there is to know about sleep, but with our current knowledge, try to aim for a few proper sleep cycles so your body and brain have time to rest, repair and prepare for the next day.