My Doctor Is a Terrible Thing

I have two heads, one human head and one ghost head. I was a human during the day and a ghost at night. In order to survive, I could only continue to take in ghost substances, but unexpectedly, I was regarded as a monster by others and was sent to a mental hospital. Unexpectedly, after I arrived here, I gradually changed from a patient to a doctor, and I began to find that none of these patients seemed to be human...