Apparently one can have such a severe mental/emotional/physical breakdown as to lose the powers of speech temporarily. I suppose there was a part of me that always knew it was possible, but it is quite a different beast to have it happen to one's self. I would have to say it was an experience akin to when you fall down on your back hard and lose your breath. Your mouth opens, but absolutely nothing can come out (although, in my experience, it has been the case that when you lose your breath due to falling poorly one is typically trying to open one's mouth and have something come -in-).
When I was finally able to force speach out at all (as obviously the person who was causing me this distress was getting further upset at my lack of ability to communicate), it was the most uncontrollable and severe stuttering I've ever heard or experienced. If you've seen One Flew Over the Cuckoo's Nest (fantastic movie, by the way; everyone should see it at least once), it was about on par with how Billy spoke or even a bit worse.
I think the involuntary body shaking was likely the least unpleasant part of it all. Fascinating what the mind causes the body to do.
I do wonder, in retrospect, whether going mute was a psychological trigger born out of fear of saying The Wrong Thing and causing the situation to deteriorate further, or if it was more of a physical-based Body Just Shutting Down Now Sorry kind of response.