I can't believe I didn't know about this until my thirties. They should be teaching it in school. Once you understand what the vagus nerve does and how concussion affects it, so many things about your recovery start to make sense.
What the vagus nerve is
The vagus nerve is the longest cranial nerve in the body. It runs from the brainstem all the way down through the neck, chest, and abdomen, branching out to connect with the heart, lungs, gut, and most major organs. It is the main highway of the parasympathetic nervous system, the rest, digest, and restore branch.
Your autonomic nervous system has two components that are constantly in dynamic balance:
- Sympathetic nervous system, fight or flight. Activates when you're stressed, threatened, or exerting yourself. Raises heart rate, increases alertness, releases stress hormones.
- Parasympathetic nervous system, rest and digest. Activates when you're safe and calm. Slows heart rate, promotes digestion, supports recovery and repair.
The vagus nerve carries signals in both directions, from brain to body and body to brain. Around 80% of its fibres carry information upward, meaning your body is constantly informing your brain about its state, not just the other way around.
What concussion does to vagal function
Traumatic brain injury, including concussion, can disrupt vagal tone, which is essentially how well the vagus nerve is doing its job of regulating the system. When vagal tone is reduced, the body has more difficulty shifting between states. It gets stuck in sympathetic activation, running high, hard to settle, slow to recover from stress or stimulation.
This helps explain several common post-concussion experiences: why you might be easily startled, why a single difficult interaction can wipe out the rest of your day, why rest doesn't always feel restorative, and why your symptoms can seem to spike from things that seem minor from the outside.
Things that help stimulate and support the vagus nerve
- Slow, extended breathing, especially extending the out-breath (see the Breath article)
- Cold water on the face, triggers the dive reflex, activating the parasympathetic system rapidly
- Humming, singing, or chanting, the vagus nerve passes through the vocal cords; vibration directly stimulates it
- Meditation, particularly body-scan and breath-focused practices
- Gentle exercise, walking, swimming, yoga
- Physical therapies, craniosacral therapy and cranial osteopathy in particular
- Social connection, safe, warm relationships genuinely regulate the nervous system via the social engagement system
- Time in nature, consistent evidence that natural environments reduce sympathetic activation
Ally's experience
The ensuite story, and why it took three days to recover
A couple of years ago I was getting ready in the morning in our ensuite, which has a laundry chute down to the downstairs. I was relaxed, listening to music. My husband and son thought it would be hilarious to lift my son up the chute and say hello. I got the biggest fright of my life.
I'm not exaggerating, it took me three days to fully recover. Three days of headaches, feeling jittery, being on edge, going for long walks just to try to unwind my system. For most people, a fright like that resolves in an hour. For me, it spiralled into three days of feeling genuinely unwell.
At the time I found this humiliating and baffling. Understanding the vagus nerve and reduced vagal tone, the difficulty my nervous system has in switching out of fight-or-flight once it's activated, made it make sense. It wasn't weakness. It was a damaged communication system doing its best.
I've also had the classic experience of working hard in the lead-up to a holiday and then getting sick the moment I stop. That's the same mechanism. While you're running on sympathetic activation, stress hormones suppress illness. The moment you finally rest, the body goes "finally, let me deal with all of this." Understanding that doesn't make it less frustrating, but it does mean I can plan for it rather than be blindsided.
The things that have made the most difference for my vagal tone over time: craniosacral therapy, daily meditation, and genuinely protecting rest rather than pushing through it.