Deep Sleep vs Light Sleep. What are the Stages of Sleep?

Woman sleeping with cat on bed

Good sleep is as vital for emotional, mental and physical health as good nutrition and exercise. And yet most of us don't understand sleep very well or value it nearly enough. A worrying number of people report difficulties getting to sleep, or sleeping through the night. Many more report waking feeling unrefreshed. The first stage in improving sleep is understanding a little more about it.

The Stages of Sleep

Since the Nineteen-Fifties, when scientists realised that sleep is neither a passive or uniform process, a lot of research has been done to understand the different stages and types of sleep. You may have heard people talking about deep sleep vs light sleep. It is now recognized that there are five different sleep stages. A healthy sleeper will cycle through each of these stages several times a night.

Light SleepSleep Stage 1

The initial stage of sleep is the lightest of all. An EEG will register only slightly slower brain waves than in the waking state, breathing rate is unchanged and skeletal muscles still have tone. At this point, the sleeper may still be aware of sounds around them, and it is in this transitional stage that people report involuntary muscle jerks and the sensation of falling. This transitional sleep stage generally lasts for 5 to 10 minutes before the sleeper passes onto stage two.

Sleep Stage 2

Nearly half of a typical night's rest may be spent in sleep stage 2. This is still a version of light sleep but with marked physiological changes. Brain waves slow down further but there are bursts of waves known as sleep spindles. Body temperature drops and heart rate slows. There is no eye movement and muscles become more relaxed. This part of the sleep cycle is associated with processing of memories and emotions, and regulation of metabolism.

Deep Sleep Stages

Both sleep phases 3 and 4 are classed as deep sleep. This is sometimes known as delta sleep in reference to the characteristic brain wave pattern associated with it. Muscles are deeply relaxed. An individual in deep sleep can be very hard to awaken. Studies have shown that someone in deep sleep can remain asleep even when exposed to noises of over 100 decibels. People waking directly from this sleep stage will generally feel very groggy, with reduced mental performance for anything up to half an hour after waking.

There is still much that we don't understand about deep sleep, but we do know that this is the time when the body is repaired, recharged and cleansed. Growth hormone is released in deep sleep (this is one of the reasons why teenagers need so much sleep and are so notoriously hard to wake up!). Cell rebuilding and repair takes place during sleep stages 3 and 4. The kidneys are more active, removing toxins built up during the day. Some doctors suggest that inadequate deep sleep reduces the efficiency of the immune system. In short, deep sleep is absolutely vital for physical health and you'll suffer if you don't get enough of it.

What prevents deep sleep? As you might expect, depression, stress or anxiety can all interfere with sleep cycles, and certain drugs or medications including caffeine can have the effect of reducing deep sleep in favour of the lighter stages. Lack of a good sleep routine can also disrupt natural sleep patterns so a quiet, calm and safe environment is vital. If you're trying to sleep in a noisy place, or somewhere you don't feel comfortable or safe, the body resists the vulnerability associated with deep sleep.

Man sleeping deep

Sleep Stage 5 - REM sleep

This is the stage most people have heard of, but what is REM sleep and why do we need it? REM stands for rapid eye movement, which is the strongest sign that someone has entered this part of the sleep cycle. Apart from the eyes, the body is very inactive during REM sleep and people waking suddenly from this phase of sleep may experience 'sleep paralysis', which is temporary but can be very frightening. We do most of our dreaming during REM sleep and this is vital for memory and emotional processing. This is also the stage when protein production in cells peak, so REM sleep is important for body maintenance and repair.

Woman Asleep

Sleep Throughout the Night

During the course of a healthy night's sleep, the sleeper will pass through all stages of sleep several times, in cycles. How long is a sleep cycle? Well, the average is around 90 minutes but some cycles can be as short as 50 minutes.

Both sleep cycle length and the amount of time spent in different types of sleep vary across individuals, and at different stages of the night's rest. Typically, in the first cycle of the night a sleeper passes through the light stages, then relatively quickly moves on to deep sleep, then through to 10 minutes or so of REM sleep, before starting the cycle again. As the night progresses, each cycle contains less deep sleep and greater amounts of light and REM sleep.

After a 'good night's sleep' and when the sleeper is able to wake naturally, they will do so from light sleep and awaken feeling refreshed. A late or disturbed night's sleep, followed by a harsh awakening by an alarm clock can result in the individual being forced to wake from deep sleep, with all the grogginess and disorientation that accompanies this.

If you're struggling with your own sleep patterns, there is a lot of help available. Good sleep hygiene, a regular routine, and even relaxation training can all be helpful. Many modern sleep aids will even allow you to monitor your own brain activity so that you can understand how much of each type of sleep you're getting, and provide cues that help you learn to train yourself to sleep better. Medications are available if all else fails, but in many ways, these are a treatment of last resort. Whenever possible, you'll benefit much more from uncovering the reasons for your sleep difficulties and addressing them, than you will from taking a tablet.

Henry Warren I am a professional writer and health & wellness enthusiast.