I wussed out.
I did not cancel the appointment [1].
Over the past few months of dealing with Bunny's medical issues, the wait for appointments was excruciating and in light of that, I just couldn't cancel someone else's appointment. Also, I thought about it, and it could have been a transcription error on the part of the doctor's office. My name can be spelled “Sean,” “Shawn,” “Shaun,” or “Shon.” My last name can be spelled “Conner” or “Connor.” That's eight combinations—more if you accept “Konner” or “Konnor” (it's not out of the realm of possibility—I had an uncle [2] whose last name was “Kollins,” not “Collins”).
I did call and this time, it was escalated to the head nurse at the doctor's office. It turns out it was a transcription error, so there's at least one explanation for receiving some other Sean Conner's email (and for the record, the head nurse could neither confirm nor deny the patient's name was “Sean Conner” even though that was clearly the case).