a quick update:
I am back on Amitryptilin (only 10mg per day), which seems to help.
I am free of symptoms now, except when I obsess about, which happens in the evenings, but talking with friends helps, I even have some completely symptom free days now. Sometimes I have trouble finding specific words, which makes me mad, because I instantly attribute every lapse of my brain to my concussion.
For the future I plan to do Autogenic training to cope with my anxiety problems and to relax, did anyone here try that?