Yah I experience something sorta similar. When I get an impact to my head it would immediately cause this very specific feeling. It was like this sick nauseaus feeling and feeling a little faint and like I wanted to rest. Generally this feeling would go away the next day or after a couple days. This is what pushed me to quit contact sports. I had one definite concussion and many of these smaller impacts btw.

However, this was caused by an actual impact (dunking the ball and throwing it through the rim directly into my head, being elbowed hard, hitting head on boards, etc)

If I slightly bump my head on something now nothing happens unless I focus on it and start worrying and then my anxiety kicks in and causes symptoms.

Ive also had many problems with walking that you can read about in my old posts. I've reduced my walking to simply what I'm comfortable with and what I have no choice but to do in my day to day life and activities. This has helped.

So how hard are the bumps your talking about? If it's relatively hard ones that cause you problems then Id say it's fairly normal but if it's really soft impacts you would have never worried about before your last concussion then I'd say it more anxiety related.

Could you go more into detail about your concussions, how you got them, how bad, did you get knocked out,etc?

Are you seeing or have you seen doctors to tell them about your problems? If not I think you definitely should.