**Core Concept**
NREM sleep is one of the two main stages of sleep, characterized by reduced body temperature, slower heart rate, and decreased brain activity compared to REM sleep. This stage is crucial for physical restoration and memory consolidation.

**Why the Correct Answer is Right**
NREM sleep is associated with the release of growth hormone, which helps in muscle growth and repair. It also plays a significant role in the regulation of the body's autonomic nervous system, promoting relaxation and reducing stress. During NREM sleep, the brain's parasympathetic and sympathetic nervous systems are balanced, leading to a decrease in cortisol levels and an increase in melatonin levels, which help in regulating the sleep-wake cycle.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might be tempting, but it is incorrect because REM sleep is actually associated with vivid dreams, increased brain activity, and memory consolidation, not NREM sleep.

**Option B:** This option is incorrect because while both stages of sleep are essential for physical and mental restoration, they have distinct characteristics and functions.

**Option C:** This option is incorrect because while sleep stage transitions do occur during the night, NREM sleep is not specifically associated with these transitions.

**Clinical Pearl / High-Yield Fact**
It's essential to note that NREM sleep can be further divided into three stages: N1, N2, and N3, with stage N3 being the deepest and most restorative stage of NREM sleep.

**Correct Answer: D. NREM sleep is associated with the release of growth hormone, which helps in muscle growth and repair.**