**Core Concept**
Atypical depression is a subtype of major depressive disorder characterized by mood reactivity and two or more of the following symptoms: increased appetite or weight gain, excessive sleepiness, heavy or leaden feeling in the arms and legs, long-standing pattern of sensitivity to interpersonal rejection, or chronic feelings of guilt or worthlessness.

**Why the Correct Answer is Right**
Atypical depression is often associated with increased appetite or weight gain, excessive sleepiness, and a heavy or leaden feeling in the arms and legs. These symptoms reflect a more reactive and sensitive mood to interpersonal rejection. The presence of mood reactivity is a key distinguishing feature of atypical depression from melancholic depression.

**Why Each Wrong Option is Incorrect**
**Option A:** Increased appetite or weight gain is actually a feature of atypical depression, making it a correct option.
**Option B:** Excessive sleepiness is also a characteristic of atypical depression, so this is not the correct answer.
**Option C:** The heavy or leaden feeling in the arms and legs is another symptom of atypical depression, making this option incorrect as well.

**Clinical Pearl / High-Yield Fact**
When diagnosing atypical depression, remember that mood reactivity is a crucial feature that distinguishes it from melancholic depression. Patients with atypical depression may exhibit increased appetite or weight gain, excessive sleepiness, and a heavy or leaden feeling in the arms and legs.

**Correct Answer: C. The heavy or leaden feeling in the arms and legs is a feature of atypical depression.**