You need to teach yourself that touches, taps and even bumps and hits to your head are not injuries in most situations. CBT therapy could help. You will likely need somebody to help but as the saying goes, You need to be willing to change.

This could be a start. Sit with your eyes closed. Have someone touch your head with an object. Relax and breath through your response. Have them touch you with more force. Relax and breath through your response.

They could lightly slap the side of your head with a lightly rolled newspaper.

As I said earlier in this thread. You have caused your brain to memorize your anxiety response. You need to teach it to memorize a non-response.

Have a pillow fight. Have a water balloon fight. Neither will cause a concussion but can startle you and lead to anxiety.

What happened when your 'barely hit my head' ?