I am not sure how they do it in Germany, but in the US, you do need a diagnosis for them to bill your health insurance. That's for any doctor or therapist. However, I did have a therapist who told me she usually just puts "adjustment disorder" which is kind of a vague way of saying someone needs help adapting to change. She doesn't usually use things like major depressive disorder or bipolar disorder. For medication, we need a diagnosis as well.