I am thrilled to report that as of Thursday evening, my cat, Callie, was showing signs of improvement.  By Friday, she was almost back to normal, and by Saturday, she was her usual self.  I am so thankful she pulled through this.  We still have no idea what caused it, other than some type of toxin perhaps.  I just hope she avoids it in the future!  She will also be pretty strictly indoors now!