**Core Concept**
When a standing person lies down, the body undergoes a rapid physiological change due to the reduction in venous return to the heart. This is primarily attributed to the effects of gravity on blood distribution within the body.

**Why the Correct Answer is Right**
Immediately after lying down, there is a significant increase in venous return to the heart. This is due to the fact that gravity no longer opposes the flow of blood back to the heart, allowing for a more efficient return of blood to the central circulation. As a result, the heart receives a greater volume of blood, leading to an increase in cardiac output.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a direct consequence of a person lying down. While changes in body position can affect blood distribution, this option does not accurately describe the immediate physiological change that occurs.

**Option B:** This is incorrect because the decrease in peripheral resistance is not an immediate consequence of lying down. While changes in body position can affect peripheral resistance, this is not the primary physiological change that occurs immediately.

**Option C:** This option is not a direct consequence of a person lying down. While changes in body position can affect blood pressure, this is not the primary physiological change that occurs immediately.

**Option D:** This option is not directly related to the physiological change that occurs when a person lies down.

**Clinical Pearl / High-Yield Fact**
When a person lies down, there is a rapid increase in venous return to the heart, which can lead to an increase in cardiac output. This is why it's essential to ensure adequate venous return when administering medications that can affect cardiac output, such as vasodilators.

**Correct Answer: C. Cardiac output increases due to increased venous return.**