Why You Can't Sleep and How Heat and Cold Might Be the Answer

Wellness | 7 min read

Poor sleep is one of the most common complaints of modern life. Around one in three adults in the UK report regularly not getting enough of it. We lie awake at night with a restless mind, wake in the small hours unable to settle, or drag ourselves through the day on four or five broken hours, relying on caffeine to paper over the cracks.

We know sleep matters. What's less understood is why so many of us struggle with it and what we can actually do that goes beyond sleep hygiene tips and chamomile tea.

The answer, increasingly supported by research, may lie in something far more elemental: the relationship between your body temperature and your nervous system. And that's where the sauna and the ice bath come in.

Sleep Is a Temperature Story

Most people think of sleep as something that happens in the mind. But it begins in the body, specifically, in a drop in core body temperature.

In the hours before sleep, your body naturally begins to cool itself. Blood vessels near the skin dilate to release heat outward. Core temperature falls by around one to two degrees Celsius. This thermal shift is one of the primary signals your brain uses to initiate sleep, triggering the release of melatonin, slowing heart rate, and easing the nervous system into rest.

This is why a cool bedroom helps you sleep. It's why warm hands and feet (a sign the body is successfully venting heat) are associated with faster sleep onset. And it's why anything that disrupts this cooling process, a warm room, alcohol, a late evening screen session, or a chronically overactivated nervous system, can make falling asleep so difficult.

Understanding this gives us something powerful: a lever we can actually pull.

How the Sauna Prepares the Body for Deep Sleep

Spending time in a traditional wood-fired sauna raises your core body temperature significantly, by two to three degrees in a typical session. This feels demanding on the body, because it is. Heart rate rises. Blood vessels dilate. Your system works hard to regulate itself.

But the magic happens afterwards.

As you leave the heat and begin to cool, your body doesn't just return to baseline, it overshoots it. Core temperature drops below its pre-sauna level, pulling you into the same thermal valley that naturally precedes deep sleep. The nervous system, which has been through a full cycle of activation and recovery, settles into a state of genuine calm.

The research backs this up clearly. A 2019 meta-analysis published in Sleep Medicine Reviews found that passive body heating, including sauna use, significantly improved both sleep onset and sleep quality, particularly slow-wave sleep, which is the deepest and most restorative stage. Slow-wave sleep is when the body repairs tissue, consolidates memory, and regulates hormones including cortisol and growth hormone.

Regular sauna users consistently report falling asleep faster and waking less frequently through the night. Many describe a particular quality of tiredness after a sauna session, not the wired exhaustion of a stressful day, but a deep, settled heaviness that makes sleep feel natural and inevitable.

There's something to be said, too, for the environment itself. Sitting in a wood-fired sauna, listening to the crackle and tick of burning logs, watching the light change through the steam, this is a profoundly analogue experience. No notifications. No demands. Just warmth, breath, and time slowing down. For many people, this hour of genuine disconnection is as valuable as the physiology.

The Role of the Cold Plunge

Cold water immersion might seem counterintuitive as a sleep aid. It's activating, invigorating, often described as the opposite of relaxing. But its effect on sleep quality is well established and the mechanism is interesting.

The cold shock of immersion triggers a sharp activation of the sympathetic nervous system, the fight-or-flight branch. Heart rate spikes. Breathing quickens. But as you breathe through it and stay in the water, something shifts. The body begins to regulate, and the parasympathetic nervous system (rest-and-digest) starts to reassert itself.

This cycle of activation and recovery is, in effect, a workout for the Vagus Nerve. The Vagus nerve is the primary conduit of the parasympathetic nervous system, and its tone, how well it can bring the body back to calm after stress, is one of the strongest predictors of sleep quality. People with high vagal tone fall asleep faster, sleep more deeply, and recover more effectively from disruption.

Cold immersion also drives a significant release of norepinephrine, up to three times baseline levels, which has a pronounced anti-inflammatory effect. Chronic low-grade inflammation is increasingly implicated in insomnia and poor sleep architecture. Reducing it, even temporarily, may help shift the conditions that make sleep difficult.

And there's the psychological dimension again. Choosing to get into cold water, breathing through the discomfort, and emerging on the other side, this builds a quiet confidence in your own nervous system. A sense that you can handle discomfort, that the body will regulate, that things will pass. That quality of equanimity is not incidental to good sleep. It's central to it.

Contrast Therapy and the Sleep Cycle

When sauna and cold plunge are combined in a single session (moving between heat and cold two or three times) the effect on the nervous system is cumulative. The body cycles between states of activation and recovery repeatedly, finishing in a deep parasympathetic calm that many describe as the most relaxed they feel all week.

Cortisol, the primary stress hormone and one of the main culprits in sleep disruption, is measurably reduced following contrast therapy sessions. Endorphins and dopamine are elevated. The body has been genuinely worked and genuinely rested, not in the passive, incomplete way of an evening on the sofa, but in a way that registers at a cellular level.

The thermal drop that follows a contrast session also mirrors and amplifies the body's natural pre-sleep cooling process. If you time your session for the late afternoon or early evening, you're essentially setting your body up for its best night's sleep.

Building a Sleep Practice at Siidde

One session can leave you sleeping more deeply than you have in months. But like most things that are genuinely good for you, the real benefits compound over time.

Regular contrast therapy appears to recalibrate the nervous system, gradually lowering baseline cortisol, strengthening vagal tone, and reestablishing the body's natural temperature rhythms. People who make it a consistent practice often find that their sleep improves not just on the nights after a session, but across the week as a whole. The body learns, over time, what deep rest feels like and begins to find its way back there more readily.

At Siidde, we offer sauna and ice bath sessions in a peaceful rural setting beside a small lake in the North West of England. After your contrast session, you're welcome to sit by the campfire, one of the most naturally settling environments the human nervous system knows. There's no rush, no schedule to return to. Just the fire, the water, and the quiet.

Whether you're dealing with chronic insomnia, the fractured sleep of a busy life, or simply a feeling that you never quite wake up refreshed, booking a regular session at Siidde could be one of the most straightforward and enjoyable things you do for your health.

Your body already knows how to sleep deeply. Sometimes it just needs reminding.

Sessions at Siidde are available for individuals, couples, and small groups. We recommend booking a recurring session, weekly, to build a consistent rhythm and experience the longer-term benefits.