**Core Concept**
Depression is a complex mood disorder characterized by persistent feelings of sadness, hopelessness, and a loss of interest in activities. It involves alterations in neurotransmitter systems, particularly serotonin and norepinephrine, which play a crucial role in mood regulation.

**Why the Correct Answer is Right**
Depression is characterized by a range of cognitive, emotional, and behavioral features, including persistent sadness, loss of interest, changes in appetite or sleep, fatigue, feelings of worthlessness or guilt, and recurrent thoughts of death or suicidal ideation. These symptoms are often accompanied by significant distress or impairment in social, occupational, or other areas of functioning.

**Why Each Wrong Option is Incorrect**
**Option A:** While this option may be a feature of depression, it is not specific and can be seen in various other conditions as well.
**Option B:** This is a common feature of depression, characterized by a lack of interest or pleasure in activities that were once enjoyed.
**Option C:** This is not a characteristic feature of depression; it is more commonly associated with anxiety disorders.

**Clinical Pearl / High-Yield Fact**
Depression often co-occurs with other medical conditions, such as diabetes, cardiovascular disease, and chronic pain, making it essential to consider these comorbidities when assessing patients with depression.

**Correct Answer:** C.