Donna,
Good points. Really, I think instructors are under the microscope at all times. Students do sense irregularities, even small, subtle changes, and some may (mistakenly) take these moods or changes personally. To whatever degree this is true, it reinforces our need to be aware of how we present ourselves. Certainly if an instructor arrives less than fully prepared, students will notice. They may not say anything (unless it is habitual), but they notice.
Barry Westling
