Is this concussive?
 

I was riding in the back of a car earlier today, on the freeway (about 70 mph), when the driver was attempting to change lanes (the lane to the left) but thought a car was in the way and immediately swerved to the right, back into the original lane. This was a very short and rapid swerve to the right while maintaining a very high speed, to where it felt like the car was almost going to roll over. I've had quite a few symptoms since the incident, but I'm wondering if it could be a new concussion?

The closest thing I could find on it was this:

(If you are in a vehicle moving forward and another vehicle T-bones you, the sudden movement of your brain changing from forward motion to sideways motion could cause a concussion.)

A fast swerve is very different from a T bone impact. The impact is the major factor.
You might get neck soreness and tightness from a quick swerve.
What symptoms are you having?

I don't know what symptoms you have, but that would certainly be enough to give a person a big adrenaline rush = fear, anxiety.

Thanks. I've been having both head and neck pain, forgetting things I normally remember (such as passwords, etc.), some trouble with words, sensitivity to sounds, tiredness, that general out-of-it feeling, etc.

Stop checking for symptoms. A car movement without hitting your head cannot exceed 1.7 Gs. It takes 60 Gs or more for a concussion.

If you run through the list of common symptoms looking for symptoms, your anxious brain will present those symptoms.