Klaus,
I have had a fragile head for years. I have never found anything that helps.
Any employer who refuses to accept that head jarring can be problematic has no grounds for their position.
You may do some research about sub-concussive impacts to see if you can find anything that will help with your employer.
You may find some worthwhile info at
www.tbilaw.com or
www.subtlebraininjury.com