Your Body Isn't Overreacting: Autonomic Dysfunction After Brain Injury
Written by Hollis Brennan, LPC, CSP
Companion piece for clinicians and helping professionals:
Your not overreacting
You stand up from the couch and the room goes blurry at the edges and you have to put a hand on the wall before you pass out and collapse. It feels like the blood is draining from your head and into your feet.
Another time, you are sitting still, watching something boring, and your heart is going like you just ran up stairs. Nothing happened. You feel fine, emotionally but your heart is racing.
When you take a hot shower and are absolutely exhausted and freezing for two hours. You walk to the mailbox and pay for it all afternoon. You're cold when everyone's warm, then soaked with sweat for no reason at all.
Somewhere along the way, someone in a white coat maybe looked at you kindly and said the word "anxiety" wrote you a script for medication or therapy, and you went home and wondered if it would go away.
Friends, family, care partners, survivors, let's talk about the part of your nervous system that gets confused with anxiety.
The thermostat
Your body has a management system you never think about. It sets your temperature. It decides how fast your heart beats. It moves blood up to your head when you stand so you don't gray out. It runs digestion, sweating, pupil size, and a good chunk of how you sleep.
It's called the autonomic nervous system (ANS), "autonomic" as in automatic. Like an automatic, set-it-and-forget-it thermostat.
A brain injury usually doesn't break that thermostat it does, however, scramble the wiring behind the wall.
Think of your body as a house with a thermostat. You’re sitting on the couch and the room is a comfortable 68 degrees, so nothing needs to change. After a brain injury, the wiring between the thermostat that sends the messages and the furnace's on/off switch can get crossed. The furnace turns on when you don't need it, and your heart pounds, your body heats up, and you feel awful, even though nothing is wrong in the room and you aren’t afraid. The thermostat isn’t broken though, the message gets lost and turns on the wrong switches.
From the outside, all anyone sees is heat pouring out of the vent. When you report your racing heart beat, feeling dizzy, and sweaty palms the thought "she must be panicking" is a very easy thing to conclude for most clinicians. You can instead ask them to check for Autonomic Dysfunction or the umbrella term: Dysautonomia.
*This is obviously oversimplified — you are not a building and your insula is not a thermostat. But I hope the point sticks: the problem is in the wiring.
Brain Injury and Autonomic Dysfunction
The network that runs all of this runs from deep in the folds of the cortex, down through the hypothalamus, through the brainstem, and into the spinal cord. It's long. It's distributed. Because of that it is exactly the kind of thing that gets disrupted when a brain gets shaken, blasted, or whipped hard. The results is that the damage is spread thin across a lot of connections rather than concentrated in one spot.
This is also why your brain scan can come back clean even when you have a brain injury. A clean scan does not mean nothing happened. It means the scanner is not designed to see that type of damage.
Researchers have been measuring this for a while now. Pertab and colleagues (2018) reviewed the concussion research and concluded that concussion likely does cause real, measurable changes in the autonomic nervous system. They found most consistently brain injuries cause changes in how your heart rate responds when your body is asked to change states. For example, standing up, walking uphill, or quickly adjusting your balance.
Mercier and colleagues (2022) reviewed the adult research and were honest about the limits. They found the dysfunction shows up often, but the severity and timing of ANS dysfunction remained hardly predictable. Translation: it's real, but nobody can predict how bad yours will be or how long it will last.
Hilz and colleagues (2017) found these changes can persist long after the acute injury period. That's part of why we talk about brain injury as a chronic condition rather than a thing that ends when you leave the hospital. Not to be grim, but because it means what you're experiencing two years after the initial injury is known and part of the injury, not evidence that you aren't recovering or that you have anxiety.
What this feels like from the inside
It feels like your body and you are on different pages.
It can feel like being unreliable. You said yes to the barbecue on Saturday because on Wednesday you felt okay, and now it's Saturday and you're sitting in the car in the driveway trying to decide whether you can do this.
It can feel like being on trial. Every appointment, you have to make a case that your symtpoms are real, even when they are hard to explain. You've also learned that if you cry while describing it, the whole visit becomes about the crying, not about the symptoms.
It can feel like a slow argument with the people who love you. They watch you cancel, they think you look fine, and they cannot make those two facts fit together. Eventually, somebody says something with an edge to it, with judgement laced in.
Underneath this experience, many survivors start asking themselves a small, corrosive question: Am I doing this to myself?
You're not. A miswired communication from your brain to your body (and back) is not a personality flaw!
Things that help
None of this is a cure and none of it replaces your medical team. But these are the strategies with the most support behind them, and the least downside.
Strategies:
Change positions slowly. Sit up, wait, put your feet down, wait, then stand. Pump your calves a few times first, squeeze your glutes. Boring, unglamorous, but it works.
Drink water, consistently. Dehydration makes every bit of this worse. If a provider has told you to increase salt, follow their guidance. Salt is essential for some orthostatic conditions but genuinely dangerous with some heart and kidney conditions. That's a conversation with your prescriber, not the internet.
Manage heat like it's a symptom trigger, because it is. Cooler showers. Cars pre-cooled. A cold pack on the back of the neck. Avoid standing in a hot kitchen for an hour.
Move in doses. This is the one that surprises people. Leddy and colleagues (2019) randomized adolescents after a sport concussion to individually dosed aerobic exercise kept just below the level that made symptoms worse, versus a stretching program. The exercise group recovered faster than the stretching group. The key wasn't exercise more, though; it was that each person's dose was set from their own symptom threshold. Ask your provider about concussion exercise testing. (More on that in should you rest after a brain injury.)
Pace based on your worst day, not your best one. Plan around the version of you that needs the most support, not the one who randomly shows up with energy once in a while. ANS dysregulation (or dysautonomia) is close cousins with cognitive fatigue, and the two often stack.
Track two weeks at a time. Time, position, activity, symptom, how long it lasted. This turns "I get dizzy sometimes" into documented evidence you can hand to your provider.
How to get taken seriously
Let's be specific here about how to be heard.
Bring numbers, not adjectives. Write down the numbers and what you felt. A home blood pressure cuff or a fingertip pulse reader is enough to get started:
If you can, take your pulse sitting after five minutes of rest.
Then take your pulse again one minute and three minutes after standing.
Now you can put the feeling to a quantifiable data point, for example: "My heart rate goes from about 75 sitting to about 115 within three minutes of standing, and I get lightheaded. I'd like to be evaluated for autonomic problems related to my brain injury."
That sentence does a lot of work. It names a pattern, attaches data, and asks for a specific evaluation. "I get dizzy a lot" gets sympathy and may lead you and the provider down the wrong path.
Two more things:
Say the injury out loud, every time, even if it was years ago and even if you never went to the ER. Providers cannot connect what they don't know about. If putting words to it is the hard part, learning to tell your brain injury story is a good place to start.
Ask for the provider's opinion in writing. If they think it isn't autonomic, ask them to note in the chart what they think it is instead. That's not hostile. It's how you avoid explaining this from scratch at every new clinic.
For families and care partners
You are not being asked to fix this. You're being asked instead to believe something you may not be able to see.
What helps:
Believe the cancellation. The person didn't get flaky. Their internal wiring did.
Take over the standing tasks as best you can and ask for friend's help. Cooking over a hot stove, waiting in lines, walking in the heat. These are the expensive ones.
Notice out loud, kindly. "You've gone pale, do you want to sit down?" beats "are you okay?" every time, because it doesn't help survivors assess and address.
Go to the appointment with your survivor. A second person confirming a pattern changes how a clinical visit goes. It shouldn't, but it does.
At school and at work
Accommodations here are cheap and unglamorous, and they work.
Ask for:
Water and snacks permitted anywhere.
No penalty for sitting or for taking a break.
Cooler rooms, a fan, or a seat near an open door.
Flexible start times if mornings are worst.
No timed physical exertion.
What this doesn't cover, and when to get help
We haven't covered medications, formal POTS criteria, hormone-related causes, or the overlap with long COVID and ME/CFS. Those deserve their own space.
Get urgent medical care for: Chest pain, actually fainting (not just feeling like you might), a new severe headache, confusion or trouble speaking, weakness on one side, or symptoms that are steadily getting worse instead of going up and down. If you can't tell, call your doctor right away. A racing heart without explanation is a good enough reason to be seen.
You're allowed to bring numbers and ask for evaluation again!
FAQ
Q: Why do I get dizzy when I stand up after a brain injury?
A: Standing up requires your body to quickly push blood upward against gravity. A brain injury can disrupt the system that manages that, so your blood pressure drops or your heart races to compensate. It's a plumbing and signaling problem.
Q: Why is my heart racing when I'm not anxious?
A: After a brain injury the system in charge of your heart rate can fire without a matching feeling. That said, a fast heart rate always deserves a medical check, there are other causes too.
Q: Can a brain injury cause POTS?
A: Orthostatic problems including POTS have been reported after brain injury, but we can't determine causality yet. Diagnosing POTS requires specific standardized testing, so this is something to raise with a physician rather than self-diagnose.
Q: My brain scan was normal. Does that mean nothing is wrong?
A: No. The autonomic network is spread across a lot of the brain and brainstem, and the kind of widespread disruption that affects it often doesn't show up on a standard MRI or fMRI scan.
Q: Should I rest or should I exercise?
A: Current evidence supports gentle, carefully dosed activity kept below the level that makes your symptoms worse, not open-ended rest. The right dose is specific to you and is best set with a provider who knows concussion exercise testing.
Q: Does more salt and water help?
A: Steady hydration helps most people. Extra salt helps some people with orthostatic problems and is unsafe for others, particularly with heart or kidney conditions. Get your advice from your prescriber, not from a forum.
Q: Will this go away?
A: It improves for many people, especially with graded activity and good management of triggers. For some it becomes a long-term condition that's managed rather than cured. Either way, it's real and it's treatable in the sense that it can be made much more livable.
Disclaimer: The information provided by Brain Injury Therapy is for educational purposes only and is not a substitute for medical, psychological, or legal advice. It is not intended to diagnose, treat, cure, or prevent any condition. Every person's medical and psychological history is unique, and readers should consult with qualified healthcare professionals before making decisions about diagnosis, treatment, safety, or care planning. Reading this article does not create a therapeutic relationship with Brain Injury Therapy, and the content should not be used in place of individualized evaluation or treatment. If you or someone you support is experiencing a medical or mental health emergency, call 911 or go to the nearest emergency department.
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