**Core Concept**
Postmortem hypostasis, also known as livor mortis, is the discoloration of the skin due to the settling of blood in the dependent parts of the body after death. This phenomenon occurs due to the lack of circulation and the effects of gravity on blood distribution.

**Why the Correct Answer is Right**
Postmortem hypostasis is caused by the separation of blood from the oxygenated tissues and its subsequent pooling in the dependent areas. As the body cools, the blood in the vessels coagulates and becomes more viscous, leading to its settling in the lower extremities. This process typically occurs within 30 minutes to 2 hours after death. The color change is usually a bluish-purple hue due to the deoxygenated state of the blood.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe the primary mechanism of postmortem hypostasis. While blood stasis is involved, it is not the primary cause of the discoloration.

**Option B:** This option is incorrect as it implies that postmortem hypostasis occurs due to an inflammatory response, which is not the case. The process is primarily mechanical and due to gravity.

**Option C:** This option is incorrect as it suggests that postmortem hypostasis is a result of a specific disease process. While certain conditions may exacerbate the phenomenon, it is not a direct result of a disease.

**Clinical Pearl / High-Yield Fact**
It's essential to note that postmortem hypostasis can be affected by the position of the body at the time of death. For example, if the body is found in a prone position, the hypostasis will be more pronounced in the lower extremities. This can be a useful clue in determining the position of the body at the time of death.

**Correct Answer:** D.