So I've read on here that you can't really suffer a head injury unless you hit another vehicle or are shaken violently.
But what if the driver turns to the left and then to the right really really quickly?

I'm asking because my dad was just driving me home and there was a car coming from the lane next to us and wanted to get in our lane. I guess my dad didn't really see him coming or the other guy was driving too fast but my dad turned the wheel to the left and then to the right really fast to avoid hitting him. This caused my head (and neck) to be shaken quite a bit since I wasn't prepared for it.

Of course I'm dizzy and have a headache now so I'm hoping it's just my neck acting up and not another concussion?

It's your neck and/or anxiety. The startle of such an event can trigger anxiety and symptoms. Walking down stairs has more G force up your spine that a car movement can cause unless you have a collision.

Anxiety all the way probably.

I got a headache one time watching another car hit a speed bump they most likely weren't aware of...I was walking! It was hard to get over it as well.

Bud

A concussion is just when the brain hits the skull. If the force was strong enough, yes. I had one from a an airbag. At first I did not know airbags could do that. But then my eyes hurt, my teeth started to hurt and then I could not recognize anyone I met after the crash and kept getting lost.
t first, I had all kinds of injuires and was considered a miracle until the neuro stuff hit, then the teeth, ,then eyes and now? Now I am not a miracle at all. No I am disabled and ruined.

Keep an eye on other things, like memory, can you find your way around etc......keep a diary for a few weeks. I hope you feel better.

An air bag is an impact source..it can hit you pretty hard.