Can you elaborate a bit on your story? How did you get your first 3 concussions and what are your symptoms?

It i very unlikely that you could get a concussion from braking quickly in a car (yes, I'm sure it was VERY quickly, but it takes a LOT of force to cause the physical conditions necessary for a concussion), so please don't worry that you are getting some kind of permanent structural brain damage from this.

Lots of stories of people getting symptoms from low-force events on here. Generally they end up being the result of one or more of the following three causes: 1) A panic attack 2) A migraine attack 3) Exacerbation of an existing subtle neck injury.