**Core Concept**
The patient's symptoms suggest a diagnosis of a psychiatric disorder characterized by decreased sleep, irritability, loss of appetite, weight loss, and increased energy levels, despite appearing physically healthy.

**Why the Correct Answer is Right**
The patient's symptoms are most consistent with anorexia nervosa, a psychiatric disorder characterized by a distorted body image and an intense fear of gaining weight, leading to restrictive eating habits and significant weight loss. The presence of erythema of the nasal mucosa and mild facial acne may be related to malnutrition. The patient's normal BMI is a red herring, as individuals with anorexia nervosa often have a normal or even high BMI due to muscle mass loss.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely a distractor, as there is no clear indication of a substance use disorder in the patient's history or physical examination.
* **Option B:** While the patient's symptoms may resemble those of a mood disorder, the presence of a distorted body image and restrictive eating habits is more consistent with anorexia nervosa.
* **Option C:** This option is unlikely, as there is no clear indication of a sleep disorder in the patient's history or physical examination.
* **Option D:** This option is incorrect, as there is no clear indication of a personality disorder in the patient's history or physical examination.

**Clinical Pearl / High-Yield Fact**
Anorexia nervosa is a psychiatric disorder that requires a comprehensive treatment approach, including psychotherapy, nutrition counseling, and medication, as needed.

**Correct Answer:** B.