You bring up a very important issue! Thank you for this question. What you are describing is selective mutism. Whether it be adult or child, it is still mutism. Over 90% of the individuals who have SM also have social phobia. So, I am not at all surprised that you have been diagnosed with this.
Some of the research we are presently pursuing is the biological causes of SM. There are actual physiological reasons as to why you cannot talk! Did you know that when you are anxious, the muscles surrounding your vocal cords tense up??? Our theory is that with SM children, this is so severe that mutism is the result! SO, please understand that what is happening to you is not your fault, and although you are an adult, you still suffer from SM. The reason so many more kids have SM compared to adults is that many SM kids slowly develop some coping skills to deal with their mutism, and may end up as just severely socially phobic adults. If they had gotten proper help along the way, hopefully they would have overcome much of their social phobia and mutism as an adult.
In your situation, you should most definitely be receiving therapy, and I recommend medication as well. Medication does wonders for adults with severe social phobia. Good luck to you and keep us informed!
Dr. Elisa Shipon-Blum