I'm about your age ,and within the last year I have developed a stutter as well. It's mild, but it's very much there and interferes with my daily life. Upon researching it, I have discovered that it is a "Psychogenic-Acquired Stutter." It's "a post-stress response to chronic or acute psychological disturbances in persons who have no prior history of stuttering." Within the last four years, I have been in a physically abusive relationship, had a miscarriage, and lost the love of my life in an extremely traumatic way. This was all on top of my clinical anxiety and depression. So, I'm sure that all this is the cause of my stutter. You mentioned that you have anxiety and that you feel a mental "numbness." You could very well have the same type of stutter as myself.