**Core Concept:** Insomnia is a sleep disorder characterized by difficulty initiating or maintaining sleep, leading to decreased daytime alertness and performance. Eating disorders, particularly those involving increased appetite and night-time eating, are often seen in patients with psychiatric disorders.

**Why the Correct Answer is Right:** The patient presents with insomnia and altered eating habits, specifically increased appetite and frequent nocturnal eating, which leads to skipping breakfast. This clinical picture is highly suggestive of Night Eating Syndrome (NES) or Eating Disorder Not Otherwise Specified (EDNOS). NES is a subgroup of eating disorders characterized by recurrent episodes of excessive eating, usually in the evening or night, leading to significant distress or impairment in daily functioning.

**Why Each Wrong Option is Incorrect:**

A. Obesity and weight gain are not the main presenting features in this case, as the patient does not seem concerned about her appearance or weight gain.

B. Obstructive sleep apnoea is ruled out as the patient has insomnia and increased appetite, not hypersomnia and weight loss.

C. Depression is a possibility, but the patient's lack of concern about her appearance and weight gain makes it less likely.

D. Anxiety is a possibility, but the patient's lack of concern about her appearance and weight gain makes it less likely.

**Why the Correct Answer is Right:**

Insomnia and altered eating patterns, particularly nocturnal eating and skipping breakfast, are the key features that lead to the correct diagnosis of Night Eating Syndrome (NES). This disorder is characterized by the following DSM-5 criteria:

1. Eating occurs during the evening or night.
2. The patient experiences significant distress or impairment in social, occupational, or other areas of functioning.
3. The eating episodes are not better explained by another psychiatric disorder, such as bulimia nervosa or binge eating disorder.
4. The patient does not have excessive daytime sleepiness or weight loss.

**Clinical Pearl:** Night Eating Syndrome (NES) is a rare sleep-wake cycle disorder that can be associated with psychiatric disorders like depression and anxiety. A thorough evaluation of the patient, including psychiatric assessment, is essential to identify and manage these underlying psychiatric issues. Treatment options for NES include psychotherapy, medication, and lifestyle modifications. In some cases, the underlying psychiatric disorder may require separate management.