Wow, I thought you were describing one of my days. I also work with profs and department heads at a university and when the fog hits hard it seems they all need me for something. And how stupid do I feel when I know what I want to say but just can't seem to get it out of my mouth. What I have been trying to tell myself is that I would never judge any of them for having a day like that and I feel a little better. What I have run into is that I really don't know that I am having that kind of day until I get to work and realize that I can't speak with words that make sense. I probably should go home but I just try to keep myself busy with things that I can't screw up.
You are in good company!