What is a Sleep Cycle? Understanding the Stages of Sleep

We spend around a third of our lives asleep, and it is much more than simply switching off for the night. While you're sleeping, your brain and body move through a repeating pattern of different sleep stages. Together, these stages make up a sleep cycle.

Understanding sleep cycles can help explain why you sometimes wake feeling refreshed and other times feel groggy, why you may wake several times during the night, and why getting enough sleep isn't always the same as getting good-quality sleep.

What is a Sleep Cycle?

A sleep cycle is the sequence of sleep stages your body moves through while you're asleep. These stages are broadly divided into REM (rapid eye movement) and non-REM, or NREM, sleep.

A complete cycle typically takes around 80 to 100 minutes, although sleep cycles vary from person to person and can also change throughout the same night. Most adults experience around four to six sleep cycles during a typical night's sleep.

After one cycle finishes, you generally move into another cycle, repeating the pattern until you wake up.

You can also briefly wake between sleep cycles without necessarily remembering it in the morning. These brief awakenings are normal.

What are the Stages of Sleep?

A sleep cycle consists of four stages:

1. NREM Stage 1: Falling Asleep
2. NREM Stage 2: Light Sleep
3. NREM Stage 3: Deep Sleep
4. REM Sleep

The balance between these stages changes as the night progresses.

NREM Stage 1: Falling Asleep

NREM stage 1 is the lightest stage of sleep and marks the transition from awake to asleep. Your muscles begin to relax, your breathing slows and you can be woken relatively easily. This stage is usually brief, usually only lasting 1 – 5 minutes

If you've ever experienced the sensation of suddenly jerking awake just as you were drifting off, that happened around the transition into sleep.

NREM Stage 2: Light Sleep

During stage 2, you're properly asleep, but you're still relatively easy to wake. Your body temperature drops, your heart rate slows and your breathing becomes more regular. Your brain also produces characteristic bursts of activity known as sleep spindles, which help to block outside interference from waking you up.

This stage can last around 10 to 25 minutes and can become longer throughout the night. Generally, a sleeper can spend about half of their sleep each night in this stage.

NREM Stage 3: Deep Sleep

Stage 3 is known as deep sleep or slow-wave sleep. This is the deepest stage of NREM sleep and is particularly concentrated during the first half of the night. It's much harder to wake someone during deep sleep, and being woken from it can leave you feeling groggy.

This stage is known to bolster the immune system and contributes to creativity and a greater attention span. We spend most of our time asleep in stage 3 as deep sleep. However, these stages do get shorter throughout the night, and more time gets spent on REM sleeping instead.

Stage 4: REM Sleep

During REM sleep, brain activity becomes more similar to wakefulness, your eyes move rapidly beneath your eyelids and vivid dreams are more common. Your muscles are temporarily inhibited, which helps prevent you from physically acting out most dreams.

Studies suggest that REM sleep is vital for cognitive functioning, creativity and healthy memory. It is also known for vivid dreams that can be remembered after waking up. Although dreams can occur in any stage, it’s been found to be more intense and more common in REM sleep than NREM stages.

Sleepers don’t enter a REM sleep stage until they have been in slumber for over 90 minutes. As sleep begins to get longer, REM sleep will get closer. However, if sleep isn’t elongated, it can sometimes last only a few minutes. REM periods also tend to become longer as the night progresses, meaning you're likely to spend more time in REM sleep towards the morning.

How Many Sleep Cycles Do You Need Each Night?

Most adults need around 7 to 9 hours of sleep per night, although individual requirements vary.

For many adults, this means completing approximately four to six sleep cycles. For example, someone who sleeps for eight hours may experience several complete cycles, with the amount of time spent in each sleep stage changing throughout the night.

Should You Sleep in 90-Minute Blocks?

You may have seen advice suggesting that you should plan your bedtime around 90-minute sleep cycles.

There's some logic behind the idea that waking at the end of a cycle might feel more comfortable, but you shouldn't treat 90 minutes as an exact figure. Sleep cycles naturally vary in length, and deliberately cutting your sleep short to hit a particular number of cycles can be counterproductive.

Getting enough sleep consistently is more important than trying to calculate the "perfect" time to wake up.

Why Do I Wake Up During the Night?

Waking briefly during the night isn't necessarily a sign that something is wrong. You can naturally wake between sleep cycles, and many people don't remember these brief awakenings.

The problem is when you wake frequently, stay awake for long periods, or struggle to get back to sleep.

There are many possible reasons for interrupted sleep, ranging from your bedroom environment to stress, discomfort and underlying sleep conditions.

Common Causes of Interrupted Sleep

Temperature

Being too hot or too cold can make it harder to remain asleep. Your body temperature naturally changes as part of your sleep-wake cycle, so a bedroom that's uncomfortably warm can make sleep more difficult.

Consider:

• Keeping the bedroom comfortably cool
• Choosing breathable bedding
• Using layers that can easily be removed

If night sweats are regularly disturbing your sleep, particularly alongside other symptoms of menopause or perimenopause, it's worth discussing this with your GP.

Noise & Light

Light and noise can interrupt sleep even if you don't fully wake up. Blackout curtains, an eye mask, ear plugs and a quieter bedroom can all help create a more sleep-friendly environment. The NHS also recommends making your bedroom dark and quiet when addressing insomnia.

Stress and anxiety

A busy mind can make it difficult to fall asleep and can also cause you to wake during the night. If you're lying awake thinking about work, finances, relationships, or tomorrow's to-do list, try giving yourself some time to wind down before bed.

A relaxing routine can include:

• Reading a book
• Having a warm bath
• Gentle stretching
• Breathing or relaxation exercises
• Writing down worries or tomorrow's tasks before getting into bed

Alcohol, Caffeine & Other Stimulants

Stimulants such as caffeine and nicotine can interfere with sleep, while alcohol can also disrupt the quality and structure of sleep even if it initially makes you feel sleepy.

The NHS recommends avoiding tea, coffee, alcohol and smoking close to bedtime when trying to improve insomnia.

Screen Time

Phones, tablets, televisions and computers can make it harder to switch off at bedtime, particularly when you're using them for stimulating activities. Rather than scrolling until the moment you want to sleep, try creating a period of quieter, lower-stimulation time before bed.

Needing the Toilet During the Night

Waking to use the toilet is common, particularly as people get older. Reducing excessive fluid intake close to bedtime may help some people, but frequent nighttime urination can have several possible causes. If you're regularly waking several times a night to use the bathroom, speak to your GP rather than simply assuming it's part of getting older.

Snoring & Sleep Apnoea

Occasional snoring isn't necessarily a problem, but loud snoring combined with pauses in breathing, gasping or choking during sleep can be a sign of obstructive sleep apnoea. People with sleep apnoea may wake repeatedly during the night and can feel excessively tired during the day.

If you or someone you sleep with notices that your breathing stops and starts during the night, speak to your GP. Sleep apnoea can be treated and shouldn't simply be dismissed as ordinary snoring.

When Should You Replace Your Mattress?

If you’re trying to decide if your mattress needs replacing, there are various signs to look out for:

• Visible sagging or dips
• Worn or damaged areas
• Springs that can be felt through the surface
• Persistent discomfort
• Waking with aches or stiffness that improve once you're out of bed
• Regularly needing to change position because you can't get comfortable
• Sleeping noticeably better elsewhere

If your mattress is old and you're experiencing several of these problems, it may be time to consider replacing it.

Find the Right Mattress for Better Sleep

At Linthorpe Beds, you can choose from a wide range of mattresses, including pocket sprung, memory foam and hybrid mattresses, as well as mattresses with natural fillings. All are available in a full range of standard UK sizes and firmness levels.

Whether you're looking for a softer or a firmer feel, cooling gel to help with temperature regulation, or a naturally breathable and dust resistant mattress, we have an option to suit your needs.

Explore our full range of mattresses