Fatigue, Sleep and Mental Health:

Why Fatigue, Sleep and Mood Are Connected

Chronic fatigue, poor sleep and low mood tend to travel together. Poor sleep drives fatigue, fatigue lowers mood, and low mood disrupts sleep further. Physical recovery tools that work on the nervous system, inflammation and thermoregulation can interrupt this cycle from more than one angle at once, which is why they are increasingly studied alongside standard psychiatric and sleep medicine care rather than as an alternative to it.

What the Evidence Says About Each Therapy

Hyperbaric Oxygen Therapy (HBOT) — Strong evidence

HBOT involves breathing oxygen in a pressurised chamber, increasing the amount of oxygen dissolved in your blood plasma. This is the modality with the most consistent randomised trial support in this category. A randomised trial in people with post-COVID condition found significant improvements in fatigue, sleep and psychiatric symptom scores, with benefits linked to measurable changes in brain perfusion on MRI. A one-year follow-up found the sleep and quality-of-life improvements were still present a year after treatment ended. Separate randomised trials found improvements in validated sleep, insomnia, fatigue and anxiety measures among people with chronic insomnia at high altitude and people with persistent symptoms after brain injury. Most of this evidence comes from people with a diagnosed condition rather than the general population, so the effect size may not be identical for uncomplicated tiredness.

Whole-Body Cryotherapy — Moderate evidence as an add-on treatment

At Cryo SubZero, our chamber runs at −110°C for a two-to-three-minute session. Cold exposure triggers a norepinephrine and endorphin response that has been studied specifically in mood disorders. A randomised, double-blind, sham-controlled trial of 92 adults with a depressive episode found ten sessions, added to standard antidepressant treatment, produced greater improvement in depression scores than sham sessions. A randomised crossover trial in healthy adults found five consecutive days reduced perceived stress and anxiety, with more pronounced sleep-related benefits reported in women. The honest caveat is that the literature positions this as an add-on to pharmacological treatment, not a substitute for it.

Infrared Sauna and Whole-Body Heating — Moderate, early-stage evidence

Passive heat exposure raises core body temperature, and there is a documented association between elevated body temperature and depressive states. A landmark 2016 randomised controlled trial in JAMA Psychiatry found a single whole-body hyperthermia session had a measurable antidepressant effect that persisted for six weeks. A 2025 randomised trial combining infrared whole-body heating with cognitive behavioural therapy for major depressive disorder found that the majority of participants who completed treatment no longer met diagnostic criteria for depression at final assessment. This was a small feasibility trial, so it should be read as promising rather than definitive.

Red Light Therapy (Photobiomodulation) — Emerging evidence

Photobiomodulation uses red and near-infrared light to influence mitochondrial activity in tissue. A 2026 systematic review and meta-analysis found modest improvement in Pittsburgh Sleep Quality Index scores compared with sham treatment, though the researchers flagged wide confidence intervals and called for more precise trials. A separate placebo-controlled trial in people with mild sleep complaints found that a specific higher dose of near-infrared light improved mood and reduced drowsiness, while lower doses did not show the same effect. Dose matters here more than most marketing suggests.

Evidence at a Glance

What This Means Practically

Trials in this space generally used five to ten consecutive sessions before measuring results. A single session may change how you feel for a few hours. A structured block over one to two weeks is what the evidence actually reflects, which is also how we structure programs at Cryo SubZero rather than selling one-off visits as a fix.

Build a Structured Recovery Plan

Feeling wiped out, sleeping badly, or just running on empty? We built Cryo SubZero around therapies with genuine trial evidence, not the latest wellness trend. Book a recovery assessment and we will map a short, structured program around what the research supports for your situation. Visit us at Level 1, 284 Bay Road, Cheltenham VIC 3192, call 03 9022 6606, or email info@cryosubzero.com.au.

Which recovery therapy has the strongest evidence for fatigue and sleep?

Hyperbaric oxygen therapy currently has the most consistent randomised trial evidence, particularly in people with long COVID, high-altitude insomnia and brain injury. Cryotherapy has solid evidence for mood and anxiety. Infrared sauna and red light therapy are promising but earlier-stage.

Can cryotherapy help with depression or anxiety?

A sham-controlled randomised trial found whole-body cryotherapy improved depression scores when added to standard antidepressant treatment. It is an add-on, not a replacement for psychiatric care.

How many sessions before I notice a difference?

Published trials generally used five to ten consecutive daily sessions over one to two weeks before measuring outcomes. Most people report subjective changes in energy and sleep within that window.

References

1. Hyperbaric oxygen therapy improves neurocognitive functions and symptoms of post-COVID condition: randomized controlled trial. PMC9276805
2. Long term outcomes of hyperbaric oxygen therapy in post-COVID condition: longitudinal follow-up of a randomized controlled trial. PMC10869702
3. Hyperbaric oxygen treatment for chronic insomnia at high altitude: a prospective, randomized, open-label, parallel-group trial. ScienceDirect
4. A double-blind randomized trial of hyperbaric oxygen for persistent symptoms after brain injury. PMC11865602
5. Rymaszewska J, et al. Efficacy of Whole-Body Cryotherapy as Add-on Therapy to Pharmacological Treatment of Depression: A Randomized Controlled Trial. Front Psychiatry. 2020. PMC7296110
6. Whole-body cryotherapy for stress, sleep and wellbeing: randomised crossover trial findings and related literature. PMC7296110
7. Janssen CW, et al. Whole-Body Hyperthermia for the Treatment of Major Depressive Disorder: A Randomized Clinical Trial. JAMA Psychiatry. 2016. doi.org/10.1001/jamapsychiatry.2016.1031
8. A Randomized Trial Testing a Novel Mind and Body Intervention for Depression: CBT and Whole-Body Hyperthermia. PMC12553885
9. Photobiomodulation and sleep quality: systematic review and meta-analysis. Lasers in Medical Science. 2026. Springer
10. Effects of Near-Infrared Light on Well-Being and Health in Human Subjects with Mild Sleep-Related Complaints: A Double-Blind, Randomized, Placebo-Controlled Study. PMC9855677