**Core Concept**
The patient is experiencing an acute panic attack, which is a sudden episode of intense fear or discomfort accompanied by physical symptoms such as hyperventilation, increased heart rate, and sweating. The most suitable treatment for acute panic attacks is benzodiazepines, which are a class of medications that work by enhancing the effects of the neurotransmitter gamma-aminobutyric acid (GABA) to produce a calming effect on the brain.

**Why the Correct Answer is Right**
Benzodiazepines, such as alprazolam (Option C), work by binding to GABA receptors, which increases the activity of GABA and results in a decrease in neuronal excitability. This leads to a reduction in anxiety symptoms, as well as a decrease in physical symptoms such as heart rate and blood pressure. Alprazolam is a short-acting benzodiazepine that is specifically approved for the treatment of panic disorder, making it a suitable choice for this patient.

**Why Each Wrong Option is Incorrect**
**Option A:** Beta blockers, such as propranolol, may help reduce physical symptoms of anxiety such as heart rate and tremors, but they do not address the underlying anxiety symptoms and may even worsen the situation.
**Option B:** Antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), are effective in treating panic disorder, but they take several weeks to start working and are not suitable for acute management of panic attacks.
**Option D:** Antihistamines, such as diphenhydramine, have sedative properties but are not effective in treating anxiety and may cause drowsiness, confusion, and other side effects.

**Clinical Pearl / High-Yield Fact**
Benzodiazepines should be used judiciously in the management of acute panic attacks, as they can be habit-forming and may cause dependence. A short course of benzodiazepines, such as alprazolam, can be used to help manage acute symptoms, but long-term treatment should be with antidepressants such as SSRIs.

**Correct Answer:** C. Alprazolam.