**Core Concept**
A transfusion reaction is a life-threatening medical emergency that can occur during or after blood transfusion. It is primarily caused by an adverse immune response to the transfused blood components, leading to the release of various chemical mediators and cytokines.

**Why the Correct Answer is Right**
The manifestations of a transfusion reaction can vary depending on the severity and type of reaction. However, the most common signs include hypotension, tachycardia, and bleeding due to disseminated intravascular coagulation (DIC). The release of histamine and other chemical mediators can cause vasodilation, leading to a drop in blood pressure. Additionally, the activation of the complement system and the release of bradykinin can cause increased vascular permeability, resulting in bleeding.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypothermia is not a direct manifestation of a transfusion reaction. While it can occur due to the transfusion of cold blood or the use of cold saline for cooling, it is not a primary sign of a transfusion reaction.

**Option B:** Hypotension is a common manifestation of a transfusion reaction, as explained above.

**Option C:** Bleeding is also a common manifestation of a transfusion reaction, primarily due to DIC.

**Option D:** Increased muscle movement is not a typical manifestation of a transfusion reaction. While muscle contractions can occur in response to the release of histamine and other chemical mediators, it is not a primary sign.

**Option E:** Decreased respiratory rate is not typically associated with a transfusion reaction. In fact, tachypnea is more commonly seen due to the release of chemical mediators and the activation of the sympathetic nervous system.

**Clinical Pearl / High-Yield Fact**
In the event of a suspected transfusion reaction, it is essential to stop the transfusion immediately and administer oxygen. The patient should be closely monitored for signs of cardiac instability, and fluid resuscitation should be initiated as needed.

**Correct Answer: C. Bleeding**