No, knuckles knocking on a door would not even be a sub-concussive impact. The skin sensation can be uncomfortable but there is no impact to the brain.

This is classic PCS PTSD. One suffers a concussion and gets sensitized to the thought of an impact to the head. The PTSD like obsession and paranoia makes one think any contact with the head is a risk.

But, the good news is these bumps have been happening all one's life and were ignored until the concussion. We just need to relearn to ignore them.

A concussion will cause an immediate visual, cognitive, awareness, balance, and/or other disturbance, not just a minor pain sensation to the skin.

Anxiety can cause many symptoms, like jitteryness, nausea, increased heartbeat, etc. These are not signs of a concussion.

Concussion induced nausea usually takes a while to manifest. Anxiety nausea is quicker to manifest.