I know a little something about going stupid-dumb. More than a little, actually. I confess that I do indeed feel qualified to address the subject. Well qualified .. with plenty of firsthand experience.
I might even be something of an expert on the subject.
The term stupid implies that you are not thinking clearly. While dumb implies that your ability to form words has somehow been compromised.
Why might you be thinking unclearly? And why might you be having trouble forming words, or putting things into words?
These are good questions.
<ignore this intentional body-text marker>