So on the way home tonight my boyfriend had to break quickly so as not to hit a dog, I didn't hit my head but since I wasn't paying attention. I didn't brace myself, after missing the dog and calming down I started to notice I had a headache and some nausea, could this be from the sudden adrenaline or do I possibly have a concussion or whiplash?

Have you had any concussions in the past?
Generally a fast/hard stop or hard braking will not cause a concussion.
If you have some head or neck injury it could aggravate that.

Ditto Jo Mar

I had a concussion at the beginning of last year and I kind of had some neck pain in early December from crumby pillows that weren't doing their job... But I am losing sleep over this I'm so afraid of brain damage or swelling that I can't sleep...

Anxious,

I've had three diagnosed concussions and have suffered from post-concussion syndrome for two and a half years now. I've had way more setbacks than I can remember, but I've never had symptoms that last more than 24 hours from anything other than a direct blow to the head.

I often used to have the same worries you do when I would brake hard in the car, or even when I would have a fit of coughing that involved moving my head rapidly. But, what I realized is that if I keep reminding myself that I've never gotten true symptoms from my head moving alone, it helps me manage anxiety, at least a little bit.

Even headbanging can damage brain but that is so insignificant because of neuroplasticity

Headbanging can severely damage the brain. There have been many instances of serious damage. Neuroplasticity has nothing to do with the damage from headbanging.