I know what you mean. I lived that for a few years.

Does the intensity of your emotional reaction increase with the intensity of the impact?

You may have other issues that increase inflammation.

The neck is a common cause of inflammation. Some claim 80% of head trauma includes symptoms caused by neck trauma.

The reading and concentrating struggle is called over-attending. The brain works hard and demands more blood flow and that can change fluid pressures in head.

Anxiety also causes extra blood flow to the head.

You may have a mix of all the above. Don't try to make sense of this. There is no linear progression in symptoms vs causes.

Your struggle with running suggests trauma to the joint between C-1 and the occipital facet of the skull. This joint can be traumatized and require years of disciplined postural choices to heal.

One of my injuries was a vertical drop that compressed my spine from my pelvis to my skull. It took years of discipline to stabilize that joint. Imaging never showed a problem but my physical therapist could tell that the joint was unstable.