Ok, I will continue with the exercises to reduce FHP.

I have tried doing the yes+no movements some more, very slowly. And I do get stiff afterwards, I can only rotate my head about 50 % of what I could before after doing these movements a couple times. From now on I am gonna be super careful about how I move my neck, unless there is a reasonable explanation as to why I get stiff afterwards. I read somewhere something along the lines of: if your spine is injured, muscle can tighten to protect it. Could this be the reason it tightens/stiffens after doing these movements?

The chiropractor I went to seemed like a quack. He did a lot of unexpected things that seemed strange to me. He he put his fingers somewhere on my chest and claimed that he checked for toxins. He slapped my back in different areas. He put his fingers on the top of my head, where I have some very tender spots, and he something along the lines of that my skull plates where locked and had to be opened up, and he said something about cerebrospinal fluid. Seems like some CST-****, which I was trying to avoid now.
I guess there are a lot of bad quacky chiropractors, but also a few good ones.

I'm thinking of going back to the physiotherapist and tell her that we should cut down on the exercises. I have a lot of trigger points over my upper body. Wouldn't it be best to get the trigger points resolved before I start to strengthen muscle?

What do you think about my neck?

Thank you so much for all your helpful replies, Mark.