Learning About What Happens During Sleep

Sleep is essential to our daily lives, playing a vital role in our ability to function and grow. Studies show that when animals are deprived of the sleep they need, they eventually die- clear evidence that sleep is necessary for survival in both animals and humans. Beyond sustaining life, sleep supports emotional regulation, promotes physical health, and enhances memory and learning. It also helps maintain optimal brain function by clearing out metabolic waste, bits of leftover material from the body’s chemical reactions that need to be removed. Throughout the lifespan, the brain’s neurons and their connections adapt, much like our sleep needs do as we grow in age, adjusting the junctions, which are connections between cells that help them stick together and communicate, between neurons in response to environmental challenges and new learning experiences.

So, how does this all work? To start, I should probably say how much sleep we should be getting per day. Sleeping takes up about one-third of our day, about 8 hours nightly. Based off of age, this is how many hours of sleep you should be getting:

• Infants need 12-17 hours of sleep
• Children need 9-12 hours of sleep
• Teenagers need 8-10 hours of sleep
• Adults need 7-9 hours of sleep
• Older adults need 7-8 hours of sleep

Once you fall asleep, a whole series of changes take place.

Let's first cover the stages of sleep during these changes that happen:

• Stage REM (Rapid Eye Movement)
• Stage NREM1 (Non-Rapid Eye Movement 1)
• Stage NREM2 (Non-Rapid Eye Movement 2)
• Stage NREM3 (Non-Rapid Eye Movement 3)

You might be thinking- What. But let's get a better understanding of this all.

Think of REM sleep as the brain’s active workshop that happens while your body is temporarily “offline.” It’s the stage of sleep where your brain is almost as active as when you’re awake; firing, processing, and reorganizing information from the day. It involves quick eye movements (hence the name) during sleep and is associated with vivid dreaming and brain activity that resembles paralysis of involuntary muscles. This just means that your body is paralyzed (except for essential muscles like your heart and lungs) so you don’t physically act out your dreams. This sleep happens in cycles of roughly 90 minutes, repeating 4-6 times per night.

Next is NREM1 sleep, which is the lightest sleeping stage, lasting only a few minutes before transferring to NREM2. Brain activity slows down, and your muscles relax.

After those few minutes comes NREM2, a deeper stage of sleep with the brain's activity slowing down more with bursts called sleep spindles and K-complexes, brainwave patterns that help with memory and keeping you asleep. Your body temperature drops, heart rate slows, and muscles relax more.

Lastly, NREM3, the deepest stage of sleep controlled by delta brain waves, the slowest kind of brainwave. This is when your body does most of its physical repair, tissue growth, and immune strengthening.

And what do all of these stages of sleep do for you, and why do you need it? When you lack both REM and NREM sleep, it can really throw off your body and mind in a big way. NREM sleep, especially the last stage, is when your body does a lot of its physical repair like I said- healing tissues, strengthening your immune system, and balancing important hormones. Without enough of this, you might find yourself feeling physically drained, more prone to getting sick, and slower to recover from any strain or injury.

On the other hand, REM sleep is critical for your brain’s emotional and cognitive health. This is the phase when your brain processes emotions, sorts through memories, and helps with learning. Missing REM sleep can lead to mood swings, irritability, and trouble concentrating or remembering things.

When both REM and NREM are insufficient, the effects compound. You might feel exhausted physically but also mentally foggy, emotionally unsettled, and less able to handle stress. Your body’s repair systems aren’t working fully, and your brain isn’t getting the rest it needs to function well. Over time, this can increase the risk of serious health issues, including heart problems, metabolic disorders, and cognitive decline. So, lacking both types of sleep is like depriving your whole system of the reset it desperately needs.

Even in the deepest sleep, we may have micro-awakenings, brief moments of waking up that we often don’t remember. If these happen too often, they can interrupt the restorative cycles and leave us feeling tired the next day.

Beyond these core stages and their functions, there are other fascinating things that can happen while we sleep. Some people experience sleep talking (somniloquy) or sleepwalking (somnambulism), which often occur during the deeper parts of NREM sleep. Night terrors, intense episodes of fear and movement without waking fully, also tend to happen in this stage, especially in children. During REM sleep, some individuals have lucid dreams, becoming aware that they are dreaming and even influencing what happens within them. I'll talk specifically about all of this in another post.

When we consistently get quality sleep, the benefits go far beyond just not feeling tired. Good sleep fuels creativity, sharpens decision-making, strengthens our emotional resilience, and supports a healthy mind and body. In short, sleep isn’t just a break from the day; it’s an active, essential process that keeps us alive, healthy, and ready for whatever tomorrow brings.