Fewer Things Better
Fewer Things Better
Ep. 188 - Sleep vs. Fatigue: The Brain Science of Two Very Different Exhaustions
We often lump every kind of exhaustion into being “tired,” but the brain doesn’t see it that way. This episode unpacks the difference between the body needing sleep and the whole system needing recovery...and why those two states feel so different. You’ll hear how late-night habits can work against us, and what it means when even long nights of sleep don’t bring relief. Most importantly, you’ll walk away with simple, science-backed ways to restore both the body and the self
Show Notes
Sleep vs. Fatigue: The Brain Science of Two Very Different Exhaustions
I just took a week-long tropical vacation. And you know what my favorite activity was? Sleeping.
Seriously. I was sleeping long every night. I was taking delicious midday naps and then, when I got back home, I slept ten hours that first night.
That’s when I realized my body was telling me something important. Rest is different from sleep. And sleep is different from fatigue. And it often takes rest to help you figure out the difference.
As busy humans, our energy cycles can follow actual seasons and also personal ones. Seasons of stress. Seasons of caregiving. Seasons when we’re pushing hard. Seasons when we’re simply holding on.
The Bottom Line on Top of this episode is that sleep is a biological cycle, but fatigue is a full system warning signal… and the remedies for each are not the same.
We use the word ‘tired’ to mean many different things. But when it comes to biology, sleep and fatigue are two different problems.
Let’s start with sleep, which is cyclical. It moves through stages with specific purposes.
Light sleep, which we have the most of, is the bridge between being awake and fully asleep. Your heart rate slows down, your breathing evens out, and your brain begins to disengage from the outside world. This stage helps filter out all the distractions and begins sorting what you learned during the day.
Deep sleep is where the most powerful physical restoration happens. This is when tissue repairs, immune function gets stronger, and your body does its heaviest maintenance work. This is when the brain’s cleanup crew, called the glymphatic system, becomes most active, it’s busy getting rid of metabolic toxins that build up during the day. And deep sleep is also critical for long-term brain health and your memory.
Then we have REM. This is a part of sleep where much of your emotional and cognitive processing is going on. When we are dreaming, REM sorts and stores our memories, its regulating our emotions, and integrating our experiences. And we need this for our own mood but also for creativity, and decision-making. That’s where the phrase “let me sleep on it” actually started.
Okay, that’s biology. Let’s look at some modern research around sleep.
When you skip or delay sleep, your internal system doesn’t simply bounce back the next day. A 2017 study showed a direct connection between sleep and our cognitive performance. Those researchers looked at the sleep of over 30,000 people in 18-months. They found that having two consecutive nights of less than six hours of sleep can leave you sluggish for up to six days. Six days.
And this short amount of sleep is something that the U.S. Army is currently running a study around sleep restriction and looking at what happens when people consistently get five or fewer hours of sleep. They call this chronic sleep restriction. What they are seeing is a measurable impact on brain function, reaction time, accuracy, emotional regulation, and overall long-term health.
That’s sleep–fatigue is different.
Fatigue is cumulative, not cyclical. It's systemic. And it is a critical warning signal.
Fatigue shows up when the entire system has been running on overdrive for too long. Too much pushing ahead, too much go, go, go.
This is when we see consistently having slower reaction times, scattered attention, brain fog, decision fatigue, lower emotional bandwidth, higher emotional response, but also that tired-but-wired feeling all at the same time.
According to the Centers for Disease Control and Prevention, more than one in three U.S. adults and nearly eight out of ten teens are not getting the recommended seven hours of sleep each night. Chronic under-sleeping is now the environment that our biological nervous systems are trying to catch up to.
This is why so many people get sick or have a physical crash when there is an actual break that’s longer than a weekend. It’s not bad timing; it’s your biology catching up.
And it’s hard for it to catch up when the tech doesn’t stop. The brain needs a genuine buffer to shift from all that digital stimulation into biological readiness for sleep.
Now our natural melatonin production starts about one to two hours before it’s dark. And as the seasons change, all that light exposure that we have once it is dark–indoor lights, anything–it can delay or disrupt our sleep quality. But really it’s that extra blue light from screens that delay the melatonin even kicking in. It keeps the stress loop open every time you see the notifications and all that endless input (even if it’s silly scrolling) it’s keeping your attention activated.
And when you sleep is almost as important as how long you sleep. Stanford University has researchers who are looking at mental health and they did a study of 75,000 people. Part of their findings were that those who went to bed earlier and woke earlier had better mental health overall, even if they naturally identified as night owls.
One explanation for this comes from what neuroscientists call the mind after midnight effect. Think of it this way–after being awake for sixteen or more hours, your brain is operating in the evening with fewer cognitive resources and fewer social guardrails. Decision-making is compromised and you’re much more likely to be impulsive (maybe you’re adding things to cart, maybe you’re watching one more episode!). The fact is your brain around midnight is not at the same battery level as it was at noon.
So what about when sleep doesn’t fix the exhaustion? This is where micro-burnout often shows up. Micro-burnout–it sounds trendy, even a little adorable, but it is the state that high-achievers can drift into when they are constantly pushing through everything and that just becomes their normal state. Episode 165 dug into this concept more, so I’ll add that link to the show notes if this feels familiar.
Overall though, sleep alone cannot reset a chronically activated nervous system.
And here is an important note: Naps, they can be great and helpful. But if you find yourself needing them regularly just to function, it may be worth seeing whether something deeper is driving that depletion. Fatigue is information, and it should be shared with your medical partners. I spent almost a full year thinking I was just tired when I was actually severely anemic. The internet can be a really helpful starting point, but it is not your doctor.
So when we come back to sleep, in addition to all the basics you already know and your Momma told you, such as don’t drink caffeine too close to bed, you can also experiment with some targeted actions that suit you.
One of my favorites is waking up with natural light or a sunrise simulation lamp instead of a jarring alarm. That gets your cortisol going before your brain is. Setting an actual bedtime and saying it out loud–I’m going to go to bed at ten-o-clock tonight–not just a general timeline like I’ll go to bed after this show or I’ll go to bed after I finish some email . Adding downtime as a feature on your apps that turns them off at least fifteen minutes before that bedtime that you’ve already identified. Also, look at your bedroom temperature, the ideal setting according to researchers is between 60 and 67 degrees Fahrenheit or 15 to 19 Celsius. And for some of you whose brains love the sounds, try some tools like binaural beats or white noise, brown noise, pink noise–there’s all sorts of things for your system.
Recovering from fatigue needs an additional plan to help with the true restoration and it takes time.
Add white space between things in your days and don’t just turn time into another productivity project. Rest needs to be a regular part of it. Even if it’s just ten minutes to get up and move in between appointments or meetings. A walk without anything in your ears, letting your brain quiet. And don’t forget about sunlight, sit somewhere where there is light and try to do it without scrolling.
Sleep is about restoring the body. Fatigue recovery is about restoring the self.
Many people move through entire seasons of life tired in ways sleep cannot touch. And when that happens, it’s not our bodies betraying us. They’re trying to communicate with us.
Whew, this was a lot of information. And that’s the purpose, it’s just information. See what resonated with you, see what you are willing to try.
You are the only expert on you.
And the more you understand what your brain and body are saying, the more instinctively, intelligently, and intentionally you can take care to take better care of yourself. Sweet dreams.