**Core Concept**
Delusion of nihilism is a type of delusion characterized by a false belief in the nonexistence of oneself or parts of oneself, or the nonexistence of the world. Early morning insomnia refers to difficulty sleeping or excessive wakefulness during the early morning hours. These symptoms are often associated with mood disorders.

**Why the Correct Answer is Right**
Major depression is a mood disorder characterized by persistent and intense feelings of sadness, hopelessness, and a lack of interest in activities. Delusions of nihilism can occur in major depression, where patients may believe that they are worthless, dead, or nonexistent. Early morning insomnia is also a common symptom of major depression, as patients often experience difficulty sleeping or excessive wakefulness during the early morning hours due to racing thoughts and rumination. The pathophysiology of major depression involves altered neurotransmitter levels, particularly serotonin and norepinephrine, which can contribute to the development of these symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Mania is characterized by elevated mood, increased energy, and decreased need for sleep. While insomnia can occur in mania, it is typically not early morning insomnia, and delusions of nihilism are not characteristic of mania.

**Option C:** Personality disorders are characterized by enduring patterns of thought and behavior that deviate from cultural norms. While personality disorders can involve delusions, they are not typically associated with early morning insomnia.

**Option D:** Schizophrenia is a psychotic disorder characterized by delusions, hallucinations, and disorganized thinking. While delusions can occur in schizophrenia, they are not typically nihilistic, and early morning insomnia is not a characteristic symptom.

**Clinical Pearl / High-Yield Fact**
Delusions of nihilism are a red flag symptom for major depression, particularly in patients with a history of trauma or previous depressive episodes. Early morning insomnia can be a useful clue in diagnosing major depression, as it is a common symptom that can differentiate it from other mood disorders.

**✓ Correct Answer: B. Major depression**