Why Your Mind Speeds Up When You Try to Sleep: The Biology of a Reactive Brain

Imagine this: you finally get into bed after a long day. You’re tired in that deep, satisfying way, the kind that should pull you directly into sleep. The room is dark, your blanket is warm, your body is ready to let go. But as the quiet settles, your mind begins moving. A small thought surfaces – something unsent, something unresolved – and suddenly you’re replaying the day, previewing tomorrow, or worrying about how tired you’ll feel in the morning. Instead of drifting, you feel yourself becoming more alert.

It’s a familiar frustration. And yet, no matter how often it happens, it still feels strangely personal – as though you’re standing in your own way. But modern sleep science tells a different story. What you are experiencing is not a flaw in discipline or mindset. It is the signature of something deeper: a measurable biological tendency called sleep reactivity.

Why the Spiral Begins Exactly When You Want to Sleep

For many people, the mind becomes loud the very moment the world becomes quiet. But this nighttime activation is not simply “overthinking.” Research shows that what disrupts sleep is not the quantity of thoughts but the orientation of them. Thoughts that focus on being awake – How long have I been lying here? Am I tired enough? What if I can’t sleep tomorrow? – are far more predictive of insomnia than ordinary worries [1, 2].

These thoughts do something meaningful in the brain. They activate the Default Mode Network, the system responsible for self-reflection, mental time-travel, and internal narration. Normally, this network begins to quiet as we transition into sleep; it’s part of how the brain shifts from outward engagement to inward rest. But when sleep-related rumination begins, this network stays active. It keeps storytelling, keeps evaluating, keeps scanning.

And when the Default Mode Network stays online, the brain remains in a mode designed for thinking rather than drifting, creating a mismatch that makes sleep feel just out of reach.The result is a paradox every poor sleeper knows: the harder you try to sleep, the more awake your mind becomes. This is the first layer of sleep reactivity: a cognitive pattern that causes the brain to grip tighter when it should be loosening its hold.

“Wired but Tired”: When Your Physiology Joins the Spiral

But mental activity is only half the equation. The body often enters the spiral too. Recent work examining pre-sleep physiology reveals that highly reactive sleepers show elevated levels of stress-related hormones, such as cortisol and CRH, in the hour before bed [3]. These hormones aren’t leftovers from earlier stress; they rise specifically during the period when the body should be relaxing into sleep.

This creates what so many people describe but can’t explain: a body that feels heavy with fatigue while the inside of the mind feels bright, jittery, or strangely alert.

This “wired but tired” state is not imagined. It reflects a coordinated mental and biological response that increases arousal at the exact moment you need the opposite. And while early evidence suggests sleep reactivity behaves like a stable trait, it remains unclear whether this predisposition is fixed or can be reshaped. Understanding this, however, helps shift the narrative: you’re not doing anything wrong – your biology is participating in the spiral.

This is the second layer of sleep reactivity: a physiological readiness that keeps the body on alert even as it longs for rest.

How Sleep Reactivity Shapes the Night That Follows

Sleep does not begin when the lights go off. It begins with a transition – a descent – during which the brain gradually shifts from fast, externally focused activity into slower, more synchronized rhythms. These low-frequency waves form the foundation of deep, restorative sleep. When sleep reactivity is high, this descent becomes harder to achieve.

Recent EEG work shows that entering sleep from a reactive, internally tense state can weaken the brain’s ability to build these strong low-frequency waves [6, 7]. Even when a wearable reports normal “deep sleep” minutes, the waves themselves may be shallower, less stable, or less restorative. Research in insomnia echoes this pattern, showing that the low-frequency activity the brain typically produces during NREM sleep can be altered even when standard sleep-stage scoring shows little change [8]. In other words, the structure of the night may look intact while the depth of the sleep within it is compromised.

Part of the reason lies in what happens just before sleep. When your mind slips into internal narration – replaying conversations, imagining tomorrow, or mentally checking how awake you feel – the brain’s default mode network, its internal storytelling system, stays active. Studies show that when this network remains engaged at bedtime, people take longer to fall asleep, wake more often, and get less efficient rest [4].

At the same time, the networks that are supposed to help the brain release wakefulness – those involved in monitoring, evaluating, and determining what matters – do not fully step back. Instead, they continue sending signals that resemble a subtle state of vigilance. Subjectively, this feels like being worn out yet internally braced, as if part of your mind is still on duty even while your body wants to rest [5]. These network-level patterns are now seen as key physiological markers of sleep reactivity: a brain that cannot fully downshift at the moment it needs to.

This explains a common frustration: you can sleep through the night and still wake up tired. The depth and quality of deep sleep depend on how the night begins  – and sleep reactivity can shift that entire trajectory.

Recognising Sleep Reactivity in Yourself

Sleep reactivity often hides behind the everyday language of “stress,” “overthinking,” or “light sleeping.” You may be high in sleep reactivity if you:

• fall asleep easily on some nights but struggle unpredictably on others
• notice your mind becomes sharper the moment you lie down
• feel disproportionately affected by small evening stressors
• wake feeling unrefreshed despite adequate duration

Seeing this pattern for what it is can be profoundly validating. It reframes your nights not as failures of willpower but as reflections of a sensitive pre-sleep state.

How You Can Support a Reactive Brain Before Sleep

The good news is that while sleep reactivity has biological roots, the state you bring into the night can be supported and shifted. And often, the most effective shifts come not from thinking differently, but from giving the brain something simple and sensory to hold onto

• Sensory grounding. Fold clothes, brush your hair slowly, or sort something small. Gentle motor activity naturally interrupts the Default Mode Network, shifting attention away from internal narrative loops.
• Repetitive low-load tasks. Hold a warm mug, touch soft fabric, or listen to a steady background hum. These simple, rhythmic sensory inputs activate external attention networks and dampen DMN-driven rumination.
• Warm-to-cool contrast. Take a warm shower and step into a cooler room afterward. This thermal shift encourages parasympathetic activation, helping the body transition out of pre-sleep hyperarousal.
• Slow-motion cleaning. Tidy your space as if you’re moving in slow motion. The deliberate pacing cues safety, reduces vigilance, and gives your mind a stable external anchor.

These approaches don’t override biology. They meet your brain where it is – reactive, alert, holding on – and offer it something gentler to hold instead.

DST’s Perspective: Better Sleep Begins Before Sleep

At Deep Sleep Technologies we believe the moments before sleep deserve far more attention than they’ve traditionally received. By the time you’re drifting toward rest, your brain is already laying down the conditions that will shape the entire night – how easily you fall asleep, how stable your sleep remains, and how deeply your slow waves will unfold.

Our work focuses on understanding and supporting this transition. A brain that begins the night in a calmer, more settled state is one that can build stronger, more resilient deep sleep. And whether through gentle guidance, better measurement, or new ways of reinforcing the brain’s natural rhythms, our goal is to help people enter sleep on steadier ground.

Because when the mind quiets and the body feels safe, sleep doesn’t have to be forced. It becomes something your brain can finally move toward with ease.

References

[1] Norell-Clarke, A., Hagström, M., & Jansson-Fröjmark, M. (2021). Sleep related cognitive processes and the incidence of insomnia over time: Does anxiety and depression impact the relationship?. Frontiers in Psychology, 12, 677538. https://doi.org/10.3389/fpsyg.2021.677538

[2] Tang, N. K. Y., Saconi, B., Jansson-Fröjmark, M., & Ong, J. C., Carney, C. E. (2023). Cognitive factors and processes in models of insomnia: A systematic review. Journal of Sleep Research, 32, e13923. https://doi.org/10.1111/jsr.13923

[3] Yu, K., Xia, L., Chen, H. H., Zou, T. T., Zhang, Y., Zhang, P., Yang, Y., Wei, R. M., Su, Z. F., & Chen, G. H. (2024). Association between sleep reactivity, pre-sleep arousal state, and neuroendocrine hormones in patients with chronic insomnia disorder. Nature and Science of Sleep, 16, 1907–1919. https://doi.org/10.2147/NSS.S491040

[4] Killgore, W. D. S., Jankowski, S., Henderson-Arredondo, K., Lucas, D. A., Patel, S. I., Hildebrand, L. L., Huskey, A., & Dailey, N. S. (2023). Functional connectivity of the default mode network predicts subsequent polysomnographically measured sleep in people with symptoms of insomnia. Neuroreport, 34(14), 734–740. https://doi.org/10.1097/WNR.0000000000001949

[5] Georgiev, T., Paunova, R., Todeva-Radneva, A., Avramov, K., Draganova, A., Kandilarova, S., & Terziyski, K. (2025). Aberrant effective connectivity within and between the default mode, executive control, and salience networks in chronic insomnia disorder-toward identifying the hyperarousal state. Biomedicines, 13(6), 1293. https://doi.org/10.3390/biomedicines13061293

[6] Bódizs, R., Szalárdy, O., Horváth, C., Ujma, P. P., Gombos, F., Simor, P., Pótári, A., Zeising, M., Steiger, A., & Dresler, M. (2021). A set of composite, non-redundant EEG measures of NREM sleep based on the power law scaling of the Fourier spectrum. Scientific Reports, 11(1). https://doi.org/10.1038/s41598-021-81230-7

[7] Ameen, M. S., Jacobs, J., Schabus, M., Hoedlmoser, K., & Donoghue, T. (2025). Temporally resolved analyses of aperiodic features track neural dynamics during sleep. Communications psychology, 3(1), 160. https://doi.org/10.1038/s44271-025-00334-2

[8] Zhao, W., Van Someren, E. J. W., Li, C., Chen, X., Gui, W., Tian, Y., Liu, Y., & Lei, X. (2021). EEG spectral analysis in insomnia disorder: A systematic review and meta-analysis. Sleep Medicine Reviews, 59, 101457. https://doi.org/10.1016/j.smrv.2021.101457