I can't speak to the PCS time frame part of it my concussion was as a teenager and I recovered without too much trouble at the time.
Although I think it did play a part in my now middle age repetitive work injuries (chronic) and minor back problems.

How did you hit your head or get your injury?
sideways impact, top of head, front or back impact?
Maybe others would have some better idea on the neck possibles.

I went flying off my horse and hit my head on the ground. I have no clue how I hit the ground or what angle I landed. I was out for however long it took my grandpa to run across the plowed field from his tractor.
All I know is as I woke up he was telling me to let go of the reins, I still was holding my horse's reins. I wanted to ride my horse home and he was jigging the whole time and I kept blacking in & out. But we were only a mile from home so we made it.