The deceleration required to cause a concussion would be so strong that you would have severely bruised your sternum (chest and ribs). You could have aggravated your neck a bit. Breaking alone cannot cause more that 1 g of deceleration, the same as laying down like you do when you go to bed.
The startle, a bit of neck discomfort and such triggered an anxiety attack and maybe a flashback of your concussion that cause your brain to replay the concussion symptoms of the past.

Take a few deep breaths. Try to relay. Find something to distract yourself from your anxious thoughts.

You will be fine.

My best to you.