Lindy,
I have had similar things happen. It's like my mouth is running faster than my brain and the result is gibberish. I have no advice other than I practice what I'm going to say in my head first and count the words on my fingers then when I say it out loud I speak slowly and count on my fingers again. It doesn't make for spontaneous scintillating conversation but at least I can make the occasional comment or response.
Not much help I know.