**Core Concept**
Catatonia is a neuropsychiatric disorder characterized by a range of abnormal behaviors, including immobility, rigidity, mutism, and automatic obedience. It is often associated with schizophrenia, bipolar disorder, and other psychiatric conditions, but can also be caused by medical conditions, substance abuse, or neurological disorders.

**Why the Correct Answer is Right**
Catatonia is typically distinguished by its presence of either immobility or excessive motor activity, often accompanied by a decrease in spontaneous speech. The exact pathophysiology of catatonia is not fully understood, but it is thought to involve an imbalance in neurotransmitter systems, particularly dopamine and serotonin. The disorder can be treated with benzodiazepines, antipsychotics, or electroconvulsive therapy (ECT).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because catatonia is indeed characterized by immobility, which is a hallmark symptom of the disorder.
**Option B:** This option is incorrect because catatonia often involves a decrease in spontaneous speech, which can range from mutism to excessive talking.
**Option C:** This option is incorrect because catatonia can be caused by a variety of factors, including medical conditions, substance abuse, and neurological disorders.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize that catatonia can present in a variety of ways, and its diagnosis may be challenging. A high index of suspicion and a comprehensive medical and psychiatric history are crucial in making an accurate diagnosis.

**Correct Answer:** A. Restlessness