If you fall asleep fine but jolt awake at 3 or 4am, or you lie in bed exhausted but unable to switch off, you don't have a willpower problem. You have a chemistry problem — and its name is the HPA axis.
It's the system behind almost every "tired but wired" night, and once you understand the loop it runs, the fix stops being "try harder to relax" and becomes something you can actually act on.
What the HPA axis is
HPA stands for Hypothalamic-Pituitary-Adrenal axis — a chain of three structures that together run your stress response. In plain terms, it's the system that decides when to release cortisol, your primary stress hormone.
The hypothalamus signals the pituitary, the pituitary signals the adrenal glands, and the adrenals release cortisol. It's a cascade, like a chain of command, and cortisol is the order that comes out the end. Crucially, this isn't only a "danger" system — it runs on a daily rhythm even when nothing's wrong.
The cortisol curve: how it's meant to work
Cortisol has a bad reputation, but you'd be in serious trouble without it. The problem isn't cortisol — it's cortisol at the wrong time. In a healthy rhythm, the curve looks like this:
- Morning: cortisol peaks shortly after you wake — the "cortisol awakening response." This is what gets you up and alert. It's supposed to be high here.
- Through the day: it gradually declines.
- Evening: it should be low, allowing your body to wind down.
- Night: it sits at its lowest, letting deep sleep happen, then begins climbing in the early hours to prepare you to wake.
High in the morning, low at night. That's the shape of a well-regulated HPA axis — and the shape that lets you sleep.
What goes wrong: a flattened, shifted curve
Chronic stress dysregulates this rhythm, and it shows up in two classic patterns that map exactly onto how stressed professionals describe their nights.
Wired at bedtime
If your HPA axis is still firing in the evening — because your brain hasn't registered that the threats are over for the day — cortisol stays elevated when it should be falling. Cortisol is an alertness signal. Elevated cortisol at 11pm is your body being told to stay ready. You feel exhausted because your sleep pressure is high, but you can't sleep because your stress system is overriding it. That's the "tired but wired" paradox in one sentence.
Awake at 3 or 4am
Cortisol naturally begins rising in the early hours to prepare you for morning. But if your baseline is dysregulated, that climb can start too early and too steeply — spiking you into full alertness at 3 or 4am, often with a racing mind that grabs the nearest worry to explain why you're awake. It feels like anxiety; it's largely a cortisol mistiming.
The vicious loop
Here's what makes this hard to break: it's a feedback loop. Stress dysregulates your HPA axis, which wrecks your sleep — and poor sleep is itself a powerful stressor that further dysregulates the HPA axis. Bad sleep raises cortisol; raised cortisol worsens sleep. Left alone, it tightens.
Which is also the good news: because it's a loop, intervening at either point helps. Lower the stress load and sleep improves; improve the sleep and the stress response calms. You don't have to fix everything at once — you just have to start unwinding it somewhere.
How to regulate your HPA axis
- Build a genuine wind-down buffer. The axis won't drop cortisol if you go from emails to pillow in five minutes. It needs a clear signal that the day's demands are over — a consistent, unhurried hour before bed.
- Get morning light. A proper morning cortisol peak helps the whole curve fall correctly later. Your circadian rhythm and cortisol curve are tightly linked.
- Protect sleep to break the loop. Since poor sleep feeds HPA dysregulation, anything that improves sleep quality also lowers the stress baseline.
- Consider adaptogens. Certain clinically studied adaptogens, such as ashwagandha, have evidence for supporting a more regulated cortisol response to stress — which is part of why they appear in well-designed night formulas.
The thread through all of it: you can't out-discipline a dysregulated stress system. You can only send it, consistently, the signals that tell it the day is genuinely over.
Tell your body the day is over
A wired nervous system keeps cortisol high when it should be falling. Moongreens is a melatonin-free night recovery drink — with clinically studied magnesium and KSM-66 ashwagandha — built to calm the stress response and support deep, restorative sleep. Manufactured in the USA, backed by a 90-night trial.
Try Moongreens →Frequently asked questions
What is the HPA axis?
The Hypothalamic-Pituitary-Adrenal axis is your body's central stress-response system. It controls the release of cortisol through a cascade from the hypothalamus to the pituitary to the adrenal glands.
How does cortisol affect sleep?
Cortisol is an alertness signal. It should be high in the morning and low at night. When chronic stress keeps it elevated in the evening or spikes it too early in the morning, it overrides your sleep — causing "tired but wired" nights and early-hours waking.
Why do I wake up at 3am with a racing mind?
Cortisol naturally rises in the early hours to prepare you to wake. A dysregulated HPA axis can start that rise too early and too sharply, jolting you awake — and the racing mind tends to follow the alertness, not cause it.
How do I regulate my HPA axis?
Build a consistent wind-down buffer before bed, get morning light to anchor the cortisol curve, protect your sleep to break the stress-sleep loop, and consider clinically studied adaptogens like ashwagandha that support a regulated cortisol response.
This article is for educational purposes and isn't medical advice. Speak to a doctor before changing how you manage your sleep.
About the author
James Higgins is the founder of Moongreens. He created Moongreens after two decades of broken sleep as a high performer with an overactive mind.