Typically when I have seen articles on sub-concussive impacts affecting the brain, it has been referring to many of them during a season. Such as heading many soccer balls, or being in many football tackles.

I don't think hitting your hand against the pillow while your head is on the pillow would come even close to the forces required for it to be considered a sub-concussive impact. But that is just my understanding of it.

I suffered and continue to suffer from anxiety, which often resulting in questions like you are asking now. You would be very surprised at the array of symptoms that just anxiety can cause.