Of course I would fall over if our superintendent walked in my class room. He rarely ever visits schools. However I have had surprise visits from our deputy supers...but never from a board member.
ON another note....Know that your bad day has happened to all of us. Take the high road! When you go in for your post-ob conference, be ready to say why it went badly. What you will do differently next time, etc. Also...sometimes a lesson will go great with one class...then horrible with another....c'est la vie!