If you get a blow to the neck, can it cause you a concussion?

I always feel very bad and confused after a small blow to the neck since the concussion (I don't think it's because of anxiety, because symptoms appear even if I don't think about it afterwards).

For example, today at the morning I was rushing to school and put on my backpack too quickly. That caused the backpack to hit the back of my neck when I put it on quickly (I put it too quickly by accident and it stroke the neck), and about 30 minutes later I started feeling confused and foggy, and also an annoying feeling like my legs are a little bit numb (difficulty walking).

Can it worsen the existing injury (cause further minor brain damage), or delay recovery of current symptoms? I'm not sure if the bad feeling I got today is related to anxiety, because I stopped thinking about it after about 10 seconds, and later when the symptoms appeared I started wondering if they are related to the hit I got from the backpack in my neck...

Does it count as a concussive/sub-concussive impact? If no, where does the limit exactly stand between concussions/sub-concussions and not concussions?

Thanks,
-ProAgonist