Dear Dr. Jung
I want to thank you for fitting me into your busy schedule on such short notice. I'm sure Dr. D's persuasion didn't leave you much choice (I would put him on your "you owe me" list).
But I am so grateful for the time you gave me performing a root canal. I was truly miserable with pain, and with a full agenda ahead of me, knew I needed immediate help.
With warm regards and many thanks -