**Core Concept**
Depression is a mood disorder characterized by persistent feelings of sadness, hopelessness, and a loss of interest in activities. The presence of sleep disturbances, such as insomnia or hypersomnia, is a common symptom in major depressive disorder (MDD). This question assesses the ability to identify a diagnosis based on a clinical presentation.

**Why the Correct Answer is Right**
The correct answer is A. Depression, as the lady's symptoms of job loss, loss of appetite, and waking up at 3 am are indicative of a depressive episode. Job loss can be a significant stressor that contributes to the development of depression. The loss of appetite is a common physical symptom of depression, and waking up at 3 am (also known as middle insomnia) is a classic symptom of depression. This is often referred to as "early morning waking" and is a characteristic feature of MDD.

**Why Each Wrong Option is Incorrect**
**Option B:** Schizophrenia is a chronic mental health disorder that primarily affects an individual's thought processes, emotions, and behavior. While sleep disturbances can occur in schizophrenia, the primary symptoms of job loss and loss of appetite are not typical of this disorder.

**Option C:** Obsessive-Compulsive Disorder (OCD) is characterized by recurring, intrusive thoughts (obsessions) and repetitive behaviors (compulsions). The symptoms described in the question do not align with the typical presentation of OCD.

**Option D:** Mania is a state of abnormally elevated or irritable mood, often associated with increased energy and decreased need for sleep. The symptoms described in the question, such as loss of appetite and waking up at 3 am, do not align with the typical presentation of mania.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that sleep disturbances, such as insomnia or hypersomnia, are common symptoms of major depressive disorder. The presence of early morning waking (waking up at 3 am) is a specific symptom that can help differentiate depression from other psychiatric conditions.

**✓ Correct Answer: A. Depression**