**Core Concept**
Anaphylaxis is a severe, life-threatening allergic reaction that occurs within minutes of exposure to an allergen, leading to a cascade of physiological responses including vasodilation, increased vascular permeability, and bronchoconstriction.

**Why the Correct Answer is Right**
The pathophysiology of anaphylaxis involves the release of histamine from mast cells, leading to the activation of smooth muscle, increased mucus production, and vasodilation. This results in decreased blood pressure, decreased cardiac output, and increased respiratory resistance. The release of histamine also leads to the activation of bradykinin, which increases vascular permeability and causes the characteristic symptoms of anaphylaxis, including flushing, swelling, and hives.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because anaphylaxis is not typically caused by a deficiency of histamine. Instead, the release of histamine from mast cells is the primary cause of anaphylaxis.

**Option B:** This option is incorrect because anaphylaxis is not typically associated with an increased heart rate. In fact, anaphylaxis is often associated with a decreased heart rate due to the vasovagal response.

**Option C:** This option is incorrect because anaphylaxis is not typically associated with a decrease in respiratory rate. Instead, anaphylaxis is often associated with an increase in respiratory rate due to the stimulation of the respiratory centers in the brain.

**Clinical Pearl / High-Yield Fact**
The "big three" symptoms of anaphylaxis are respiratory distress, cardiovascular collapse, and a decrease in blood pressure. Remembering these symptoms can help you quickly identify patients who require immediate treatment.

**Correct Answer:** C.