**Core Concept**
The question tests the understanding of digitalis, a cardiac glycoside used to treat heart failure and arrhythmias, and its side effects. Digitalis works by inhibiting the **Na+/K+ ATPase pump**, leading to increased intracellular calcium and enhanced cardiac contractility.

**Why the Correct Answer is Right**
Since the correct answer options are not provided, let's discuss the common side effects of digitalis, which include nausea, vomiting, fatigue, and cardiac arrhythmias. These occur due to the drug's effect on the **heart's electrophysiology** and **autonomic nervous system**.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option, we can't comment on its correctness, but typically, options might include common side effects like **anorexia** or **visual disturbances**.
**Option B:** Similarly, without specifics, we might expect incorrect options to include known side effects such as **confusion** or **headache**.
**Option C:** This could potentially include a less common but recognized side effect, making it incorrect as the "all except" option.
**Option D:** This might list a very rare or unrelated condition, but without specifics, it's hard to determine its correctness.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that digitalis toxicity can manifest as **bradycardia** or **high-degree AV block**, which are critical to recognize and manage promptly.

**Correct Answer:** Correct Answer: D. Diarrhea