zant,

Welcome to NeuroTalk.

A ping pong ball, if moving very fast, could traumatize a thin layer of skin but could never cause any level of concussive or even sub-concussive impact force.

A ping pong ball weighs 2.7 grams. A head weighs 5000 grams. That is 1850 times heavier. The force from a thrown ball would not be enough to do any harm. That ping pong ball will deform when it hits. This serves to reduce the already small force of the ball's impact.

You were likely startled and annoyed. This can trigger a replay of concussion symptoms that your brain has memorized from a previous real physical trauma.

You sound like you may have developed or taught yourself to be overly vigilant at avoiding any impact. This sets you up for this excessive response. It can also increase your risk level by disrupting your normal responses. Think of this as a distraction to normal protective behaviors. The additional stress can actually cause a loss of motor control/response.

You will be fine.

My best to you.