**Core Concept**
A doppelganger is a psychological phenomenon where an individual experiences a feeling of having a duplicate or second self. This concept is rooted in the realm of psychiatric disorders, particularly in the context of dissociative symptoms and anxiety disorders. The term "doppelganger" originates from German folklore, where it referred to a supernatural duplicate of a person.

**Why the Correct Answer is Right**
The feeling of a doppelganger is characterized by a subjective experience of having a second self or duplicate, which can be accompanied by feelings of anxiety, disorientation, and detachment from reality. This phenomenon is often seen in individuals with dissociative disorders, such as dissociative identity disorder (DID), where the individual experiences multiple identities or alters. The feeling of a doppelganger can also be a symptom of anxiety disorders, such as post-traumatic stress disorder (PTSD), where the individual may experience flashbacks or feelings of being in a different time and place.

**Why Each Wrong Option is Incorrect**
**Option A:** A shadow following a person refers to a phenomenon described in Jungian psychology, where an individual perceives a dark, amorphous figure following them. While this can be a symptom of anxiety or trauma, it is not the same as experiencing a feeling of having a duplicate self.

**Option C:** Identification of a stranger as familiar is a phenomenon known as Capgras syndrome, which is a type of delusional misidentification syndrome. This involves a person believing that a familiar person, such as a family member or friend, has been replaced by an identical-looking imposter. While this can be a related concept, it is distinct from the feeling of having a doppelganger.

**Clinical Pearl / High-Yield Fact**
It's essential to differentiate between the feeling of a doppelganger and other psychiatric phenomena, such as Capgras syndrome or shadow following. A thorough psychiatric evaluation, including a detailed history and mental status examination, is necessary to accurately diagnose and treat these conditions.

✓ Correct Answer: B. Feeling of double of oneself