Why Do You Feel Tired After a Hyperbaric Oxygen Session? The Physiology Behind Post-HBOT Fatigue
Lisa St. John, M.S.
Lisa is our Clinic Director and Founder. She earned her Master's degree from Harvard University, completed a Fellowship at Stanford University, and has spent the last 30 years working in the healthcare field.
You lay in the chamber for 60 to 90 minutes, breathing pure oxygen while resting comfortably — so why do you feel wiped out afterward? If you've left a hyperbaric oxygen therapy (HBOT) session feeling more tired than when you walked in, you're not alone, and you're not doing anything wrong. Here's what's actually happening in your body.
Yes, This Is a Real and Documented Response
Post-treatment fatigue after HBOT is well-recognized in the clinical literature. Research published through the National Center for Biotechnology Information (NCBI) notes that patients receiving hyperbaric oxygen therapy frequently report fatigue after several sessions — common enough that many hyperbaric programs schedule weekend breaks specifically to let patients recover before the next week of treatment.
What's Actually Happening in Your Body
It can feel strange to be tired after essentially lying down for an hour, but the explanation is physiological, not psychological.
1. Your cells are doing hard work, even though you aren't. During HBOT, oxygen dissolves into your blood plasma at levels far beyond normal — the equivalent of a significant metabolic event for your cells. Your mitochondria (the energy-producing structures inside cells) ramp up activity to use this surge of available oxygen, driving tissue repair and metabolic processes. That cellular workload draws on your body's energy reserves, even though you were physically at rest.
2. Oxidative stress is part of the healing process. A study published through NCBI examining oxidative stress markers in HBOT patients found that hyperbaric treatment activates the body's reactive oxygen species (ROS) response — a normal part of how HBOT triggers healing, but one that also requires energy to manage and neutralize. Research on pulmonary oxygen effects during HBOT similarly points to this oxidative response as a contributor to the fatigue some patients experience after repeated sessions.
3. Your body is still recalibrating from pressure changes. Time spent at increased atmospheric pressure asks your cardiovascular and respiratory systems to adapt, even during a relaxing session. That adjustment period, on top of the cellular repair work happening simultaneously, adds up.
Is This a Bad Sign?
No — in most cases, mild post-session fatigue is considered a normal response, not a warning sign. It generally reflects that your body's repair mechanisms are actively engaged, not that something is wrong. That said, fatigue that is severe, doesn't improve with rest, or comes with other symptoms (chest pain, vision changes, disorientation) should always be reported to your care team — those can be signs of a different issue and shouldn't be assumed to be "normal" without medical evaluation.
Tips for Managing Post-HBOT Fatigue
Plan lighter activities for the rest of the day after your session, especially early in your treatment course
Stay well-hydrated before and after sessions
Eat a balanced meal beforehand — your body needs fuel to support the metabolic demand of treatment
Give yourself permission to rest — many clinics build rest days into weekly treatment schedules for exactly this reason
Track your pattern — most patients find fatigue lessens as their body adjusts over the course of treatment
Safety and Expert Care
At Bay Area Hyperbarics, our team monitors every patient throughout treatment and is available to talk through what you're experiencing, so you always know what's expected and what's worth flagging.
Consult a healthcare provider before starting any new treatment. This article is for educational purposes and does not replace medical advice from your care team.
Frequently Asked Questions
Is it normal to feel tired after hyperbaric oxygen therapy? Yes. Post-session fatigue is a commonly reported and well-documented response, generally linked to the metabolic and oxidative processes involved in HBOT-driven tissue repair.
How long does post-HBOT fatigue usually last? It varies by person, but fatigue is typically short-lived, often resolving within a few hours to a day. Many patients notice it lessens as they progress through their treatment course.
When should I be concerned about fatigue after HBOT? If fatigue is severe, doesn't improve with rest, or is accompanied by other symptoms like chest pain, vision changes, or confusion, contact your care team promptly.
Have questions about what to expect from your HBOT sessions? Reach out to our team — we're happy to walk you through it.
