Sleep Science 101: What Your Body Does at Night

Have you ever wondered what actually happens to your body and brain while you sleep? Most of us know we feel better after a good night’s rest, but the real magic of sleep goes far beyond simply feeling refreshed.

Each night, your mind and body embark on a carefully orchestrated journey through distinct stages, each playing a crucial role in restoring your energy, sharpening your memory, and protecting your long term health.

In this blog, we’ll break down what happens during sleep step by step so you can understand why every phase matters and how quality rest can help you perform your best. Let’s pull back the covers and discover the science of sleep, made simple.

How Sleep Works

Sleep is a normal bodily process that, among other things, lets you remember what happened today for tomorrow, wakes you up in a better mood, and helps your body stay healthier for longer. We typically think of sleep as simply getting into bed, closing our eyes, and gently drifting off to a dream world. However, the process isn’t that simple. 

In fact, sleep is one of the most complex scientific body processes. While you read this, your brain is already planning tonight’s seven hour maintenance shift, fine tuning everything from your memory to your mood.

Our bodies set an internal clock that tells us when to sleep and when to wake up. Called our circadian rhythm, this essential process regulates our roughly 24 our sleep wake cycle. Temperature and light influence our circadian rhythm, and in turn, behaviors such as sleeping and eating.

For example, sipping morning coffee as the sun rises signals your body that it’s time to get going, while scrolling through your phone late at night under bright light can confuse your internal clock into thinking it’s still daytime. Avoid work or school related tasks at night that could trick your rhythm into its earlier in the day, making it harder to settle into restful sleep.

Sleep science tells us that certain processes only happen when we rest. Our bodies take a break during sleep, while our brains become less active. Here’s what your off duty body secretly accomplishes each night:

• Store and Conserve Energy: The cells in our bodies use a lot of resources during the day. Sleeping allows us to restock and prepare for the day ahead. Think back to the last time you hit an afternoon slump after a night of poor sleep sound familiar? That drained, foggy feeling is your body’s way of showing how important sleep is for restoring energy.
• Self repair and Recovery: We heal from injuries and repair our bodies during sleep. Hence, the reason we feel more tired when we’re sick or injured.
• Maintenance: Our brains reorganize and catalog memories and information while we sleep. Sleep helps make memories easier to retrieve.  

Listen to Catching Zzzs: Mastering Your Internal Clock: Optimizing Sleep and Health With Circadian Rhythm Insights with Ellen Wermter & Mary Helen Rogers

Sleep Cycles Explained

The restorative functions we just covered occur during two phases of sleep, non REM and REM. These phases are further divided into five sleep stages that make up our sleep cycle. One sleep cycle typically lasts 90 to 120 minutes, and most of us complete 4 or 5 cycles during 8 hours.

Before we dive into the sleep stages, note how much sleep we need at different stages of our lives. The Cleveland Clinic suggests following these guidelines:

• Newborns (up to 3 months old): 14 to 17 hours
• Infants (4 to 12 months old): 12 to 16 hours, including naptime
• Young children (1 to 5 years old): 10 to 14 hours, including naptime
• School aged children (6 to 12 years old): 9 to 12 hours
• Teenagers (13 to 18 years old): 8 to 10 hours
• Adults (18 years and up): 7 to 9 hours

Notice how our need for sleep decreases as we grow older, but never disappears entirely quality rest is essential at every age.

Phase 1: Non REM Sleep

Stage 1

The first stage of light sleep helps us transition from wakefulness and begins when we close our eyes. If we wake up, we can feel like we haven’t slept. It’s also the stage most associated with the sense of falling, a jerking or twitching condition known as myoclonus.

Stage 1 typically makes up 5% of our sleep.

Stage 2

During Stage 2, sleep onset occurs when our heart rate and brain waves slow, and body temperature decreases. We spend about 45% of our time in Stage 2 sleep; in fact, it’s the stage we spend the most time in.

Think of Stage 2 as the “bottom of the food pyramid” of sleep: it’s basic, repeated often, but essential for our daily and nightly journey. We cycle through Stage 2 multiple times each night as a sort of resting stop between deeper or dream filled stages, making it a vital foundation for restful sleep.

Stages 3 and 4

Stage 3 is NREM, and Stage 4 moves us closer to REM sleep. Being awakened during either of these stages can feel disorientating or confusing. Combined, Stages 3 and 4 constitute about 25% of our nightly sleep. Babies, children, and older adults need more Stage 3 and 4 sleep to feel fully rested.

Have you noticed children melting down without a nap or older adults heading to bed much earlier than others? These behaviors are often visible signs that they haven’t gotten enough deep sleep, highlighting just how important these stages are for mood and energy.

Our bodies can revert to Stage 2 sleep if we’re not fully ready to reach REM and deep sleep. Not getting enough sleep during these stages can leave us feeling tired and lethargic, even if we sleep for a long time.

Phase 2: REM Sleep

Stage 5

As we come out of deep sleep and enter Stage 5, or REM sleep, we begin to dream. We may also experience eye movement, an increased respiratory rate, and increased brain activity.

Have you ever felt like you couldn’t get out of a dream? This sensation can be due to voluntary muscles becoming paralyzed during REM sleep. Fortunately, this paralysis is simply a temporary protection mechanism that keeps us from hurting ourselves during REM sleep.

What Happens When You Sleep?

As mentioned above, several body and brain processes only occur during sleep. A few of the most essential include:

Brain Cleansing

Our brains store and consolidate memories, remove waste, and perform numerous critical functions during sleep. The ability to learn, form memories, focus, and react can all be affected by insufficient or poor quality sleep. We might also struggle to understand other people’s emotions and reactions. Sleep deficiencies can make us feel frustrated, cranky, or worried.

Decreases Cancer Risk

Disruptions to our sleep cycle can increase the risk of some cancers. The World Health Organization has acknowledged that disrupted circadian rhythms are a probable carcinogen.

Heart Health Improvement

Good sleep reduces the risk of high blood pressure, which is a significant risk factor for heart disease. Our sleep habits also help reduce inflammation in the cells that line our veins. Inflammation can contribute to cardiovascular disease.

Researchers at the National Institutes of Health’s National Center on Sleep Disorders Research discovered a connection between the brain, bone marrow, and blood vessels that can protect against hardening of the arteries when sleep is disrupted. Hardened arteries restrict blood flow to the heart and can lead to heart attacks or strokes.

Simply put, fewer hours of sleep can mean stiffer blood vessels, making it harder for our hearts to stay healthy.

Lowers Risk of Certain Diseases

Sleep helps maintain our brain’s ability to adapt and function properly, a process known as brain plasticity. Healthy, quality sleep can help prevent autism, schizophrenia, and dementia. Additionally, the cleaning process that occurs in our brains during sleep removes toxic proteins that can lead to Alzheimer’s disease.

Strengthens the Immune System

Microglia, the cells that improve brain plasticity, help our brains fight infections during sleep. A lack of sufficient quality sleep can make us more susceptible to illnesses and viruses and affect how quickly we recover.

Hormone Regulation

Our bodies produce different hormones throughout the day and night. Cortisol, which helps us wake up, is produced in the mornings. At night, our bodies produce melatonin, a hormone that helps us feel sleepy.

Other hormones follow 24 hour patterns that vary with age. For example, in children, gonadotropin releasing hormone (GnRH) signals the glands to release testosterone, estrogen, and progesterone at night. As puberty approaches, the pulses of GnRH become stronger.

Metabolism Regulation

In addition to regulating sleep cycles, our circadian rhythm helps control when we eat. Our bodies metabolize fat in the liver, muscles, and fat at appropriate times each day. When we eat irregularly, fat isn’t metabolized properly. Additionally, studies show that not getting enough sleep is a contributing factor to weight gain and obesity. 

Take this self check to see how your sleep habits might be affecting your weight and health:

• Are you finding yourself hungrier than usual, especially for unhealthy foods, after a poor night’s sleep?
• Do you notice cravings for fatty, sweet, or salty snacks when tired?
• Have you felt less motivated to be physically active after sleeping too little?
• Has your doctor mentioned any changes in your ability to process sugar, such as insulin resistance, at times when you are not well rested?
• Have you noticed any recent weight gain or risk factors for metabolic syndrome when your sleep has been disrupted?

Answering “yes” to one or more questions may suggest that your sleep patterns are beginning to affect your metabolism and your risk of weight gain. It could be worth speaking to your healthcare provider about your sleep habits.

Tips for Getting Better Sleep

Now that we know how sleep works, let’s talk about how to get great sleep! Experts refer to the practices and habits that contribute to a good night’s rest as sleep hygiene. Good sleep hygiene happens throughout the day, not just at bedtime.

The following practices can help improve sleep duration and quality:

• Make Time: Set a bedtime that lets you get the recommended hours of sleep each night.
• Set (and keep) a Sleep Schedule: Go to bed and wake up at the same time every day. Yes, even on weekends and during vacations.
• Design a Bedtime Routine: Plan to spend 30 to 60 minutes preparing for bed by doing relaxing activities, such as reading, listening to music or a podcast, journaling, or taking a warm bath.
• Go to Bed Tired: Don’t go to bed before you’re relaxed enough to sleep. Continue doing additional activities from your bedtime routine to help you wind down.
• Turn Off Screens and Bright Lights: Light, especially blue light from screens, can disrupt your circadian rhythm, making it harder to fall and stay asleep.
• Avoid Certain Foods and Beverages at Bedtime: Stop drinking alcohol and eating sugary or fatty bedtime snacks at least an hour or two before bed.
• Try Natural Sleep Aids: Instead of over the counter sleep medications, talk to your healthcare provider about natural sleep aids, such as herbs, supplements, and foods that can help you sleep.
• Exercise Regularly: Try to get at least 30 minutes of exercise per day and avoid strenuous exercise at least two hours before bed.
• Use Your Bedroom Appropriately: Your bedroom should only be used for sleep and intimacy. Avoid working or studying in your sleep space, if possible.

Your Body and Sleep

Prioritizing good sleep is one of the most powerful choices you can make for your health, energy, and happiness. Each night, your body and brain work together behind the scenes to restore, repair, and prepare you for the day ahead.

By giving yourself the gift of consistent, quality rest, you’re not only investing in a better tomorrow but also in your long term well being and performance. Embrace the science of sleep protect your nightly recharge, and let every morning be a fresh start toward your best self.