**Core Concept**
Caffeine withdrawal is a condition that occurs when an individual suddenly stops consuming caffeine after prolonged use. It is characterized by a set of symptoms that are opposite to those experienced during caffeine intoxication. The physiological changes that occur during caffeine withdrawal are primarily related to the downregulation of adenosine receptors in the brain.

**Why the Correct Answer is Right**
Caffeine acts as an adenosine receptor antagonist, thereby blocking the action of adenosine, a neurotransmitter that promotes sleep and relaxation. During prolonged use, the brain adapts by increasing the number of adenosine receptors. When caffeine is suddenly withdrawn, the increased number of adenosine receptors leads to an overproduction of adenosine, resulting in symptoms such as headache, fatigue, and difficulty concentrating. The correct answer is related to a feature that does not align with the known pathophysiology of caffeine withdrawal.

**Why Each Wrong Option is Incorrect**
**Option A:** Headache is a common feature of caffeine withdrawal, caused by the rebound effect of adenosine on the blood vessels in the brain.
**Option B:** Fatigue is also a characteristic symptom of caffeine withdrawal, resulting from the decreased activity of the central nervous system due to the lack of caffeine.
**Option C:** Insomnia is a feature of caffeine withdrawal, as the body readjusts to the absence of caffeine and the normal sleep-wake cycle is restored.

**Clinical Pearl / High-Yield Fact**
It's essential to note that caffeine withdrawal can occur in individuals who consume as little as 100mg of caffeine per day, which is roughly equivalent to one can of cola.

**Correct Answer: D.**