The other night while we were driving home at about 65 miles per hour, we had to stop almost immediately due to an elk standing in the road. Starting the next day, I've had concussion symptoms (headache/dizziness/fatigue/sleepiness/mental fatigue/brain fog/difficulty concentrating/feeling out of it). I did not hit my head, but I did sort of brace it/try to hold it in place while we stopped. Is it possible to get a concussion just from slamming on the brakes at 65 miles per hour?

Have you had a concussion in the past?

From past posts asking a similar question, it would be extremely rare to get a concussion that way.
As I understand it , there is just not enough force (G forces) when the head does not hit something.

If you had a past concussion and still had some symptoms from it, possibly might trigger a bit of a relapse..
Or if you had any past neck/shoulder issues, it could cause a flare up of that.

I'm with Jo*Mar. There are not enough G forces. The maximum G force from an emergency stop is about 0.9 G. That is about the same as sitting on your bed and falling back with your head landing on your pillow.

You may get some neck strain from the whiplash.

Or you may have had a poor night sleep. The anxiety of such a near collision could easily disrupt normal sleep and cause all of your symptoms. Many of us who struggle with insomnia have days full of those symptoms.

Glad you did not collide with the elk. I've lived and driven in elk and moose country for decades. It can be scary to see that dark shadow so suddenly.

btw, The safest way to drive in such situations is to brake hard and stop straight. Trying to dodge the animal causes frequent roll-overs and excursions off the road and down the embankment.

With elk or moose, there is a risk of the animal crashing through the windshield so ducking to the center of the car can be important.

But, the more important concept is to not out drive your headlights, especially in elk or moose country.

Here is an interest page of charts and explanations about braking.

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jo*mar, I did not hit my head and have pcs. I am 2 years and 4 months out, I was in a car crash oncoming car hit front drivers side and spun around and hit rear of car before going in the ditch.

I wish you could not get a concussion without hitting your head, my life would be much different!

A violent car accident with multiple impacts is quite different from a hard braking stop with no collision.
It sounds like you got impacted in many ways.
Did you get whiplash & soft tissue injuries also?

Is that 0.9G actually the amount of force against your head though? If so, why does it seem like such an extreme jolt to brake suddenly? It just seems like it would have to be at least several Gs of force. Also, my 40 pound dog flew off the back seat, could 0.9G do that?

It wouldn't even take that much. You have to remember that one G or 9.81 m/s^2 is the acceleration that is responsible for us staying anchored to the ground. I think people get confused when they think a G is a force when it's a measure of change in velocity that acts on the mass of our bodies whether it be in a car accident or just turning the head quickly.

I'm with Mark on this one. I had similar complications and they ended up being upper neck issues.

An easy way to think of 1 G in a sudden stop would be the car suddenly being tipped upright so the front bumper is on the ground and the back is straight in the air. The force felt against the seat belts would be one G. Your dog would fly forward. The G limiting factor is your tire traction. Common tires on dry pavement cannot provide more than .9 G of stopping force, usually less.

65 mph is 95 f/sec. The normal emergency stopping time at 65 is 3.5 seconds. 95 divided by 3.5 is 27 ft/sec2. One G is 32 ft/sec2. 27/32 equals .84 G.

The whiplash force could magnify this a bit but not more than a factor of 2.

It takes 20 G's for even a super sensitive brain with a recent concussion to be reconcussed. 50 to 60 G's is usually required.

My bet is you experience a traumatic event that disrupted your sleep and may have left you with a neck strain.

Thanks so much for the explanations. I dont think I did get whiplash, because I actually tried to brace myself and hold my neck/head still. Could the fact that I held my head still instead of moving it forward actually have made my brain bump my skull? Or would there still not be enough force for that to happen?

A 1 G brain against skull is of no consequence. I truly believe you need to consider the anxiety such a scare could cause. Sleep disruption can have a huge impact.

How many times have you played that elk scenario over in your head ?