After my PCS started, I noticed that small bumps are enough to cause symptoms of a concussion for a long time (a few hours or even a day).

For example, I was at a party yesterday, and a friend of mine has thrown a rice-filled ball (or a small stress-ball) and it hit me in the back of the head above the neck. It probably weighs a few hundreds of grams (it's one of these small balls that can be covered inside the head and pressed).

I immediately got startled because of this and got anxious that some damage might have occurred, but I quickly calmed myself down.

Even though it was almost a day ago, I feel some neck pain and dizziness which I didn't feel in the last few days. I don't think it's from anxiety - I calmed myself down quickly after.

Why so such small bumps cause me symptoms that you get after a concussion? That ball was maybe 300-400 grams - it was thrown in a high speed, but is it really enough to cause me a sub-concussive impact that leads to such symptoms?

If it's not an impact, so where all these symptoms come from? As I said, I get anxious because it hit me in the head pretty quick, but I quickly calmed myself so I don't think my symptoms now are related to anxiety. Could such a ball thrown to the head cause a small impact that leads to concussion-like symptoms?

Thanks,
-ProAgonist