Which symptom would be least likely in a patient with an anaphylactic reaction?

In an anaphylactic reaction, the body's immune response is severe and typically manifests through specific symptoms. Hives and swelling of the throat are classic indications that the body is reacting to an allergen, as they result from the release of histamines and an inflammatory response. Unresponsiveness can occur in severe cases where the airway is compromised or there is a significant drop in blood pressure.

Diarrhea, while it can be a symptom related to an allergic reaction in some contexts, is not a commonly recognized sign of anaphylaxis itself. The typical manifestations of anaphylaxis are respiratory distress, cardiovascular instability, and skin changes, rather than gastrointestinal symptoms like diarrhea. Thus, among the provided options, diarrhea is least likely to occur in the immediate context of an anaphylactic reaction.