Find a therapist to teach you Cognitive Behaviors to stop this irrational thinking. Bumping the wall was likely not even a sub-concussive impact. Even if it was, subconcussive impacts are harmless unless you have many in a short period, like a hour or two. I doubt you stood on the stairs and repeated that head bump into the wall over and over.

Your anxiety is more damaging that a simple bump like that.

You may want to learn to slow down with movements in confined spaces. Learn to move with purpose, not reactively.

CBT, Cognitive Behavior Therapy, is a process where you learn to redirect anxious thoughts away from the obsessive thoughts that can mess up your life.

For example, In this case, as soon as you bump the wall, you tell yourself, "That was just a bump. It was not an injury. I am fine. I will be OK. Maybe I should slow down."