**Core Concept**
Spontaneous contraction is a type of muscle contraction that occurs without any external stimulation, often due to abnormal electrical activity in the muscle tissue. This phenomenon can be observed in various muscle disorders and can be a diagnostic clue for certain conditions.

**Why the Correct Answer is Right**
Spontaneous contraction is typically seen in conditions where there is an abnormal ion flux across the muscle cell membrane, leading to depolarization and subsequent muscle contraction. This can occur in conditions such as malignant hyperthermia, neuroleptic malignant syndrome, and certain types of muscle dystrophy. In these conditions, the abnormal electrical activity can lead to spontaneous muscle contractions, which can be painful and debilitating.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while muscle cramps can be painful and debilitating, they are typically caused by external factors such as dehydration or electrolyte imbalances, rather than spontaneous contraction.

**Option B:** This option is incorrect because hypokalemia can cause muscle weakness and fatigue, but it is not typically associated with spontaneous muscle contractions.

**Option C:** This option is incorrect because myasthenia gravis is a condition characterized by weakness and fatigue of the muscles, but it is not typically associated with spontaneous muscle contractions.

**Clinical Pearl / High-Yield Fact**
A classic exam trap is to confuse spontaneous contraction with other types of muscle disorders, such as muscle cramps or myasthenia gravis. To avoid this, remember that spontaneous contraction is typically associated with abnormal electrical activity in the muscle tissue, leading to depolarization and subsequent muscle contraction.

**Correct Answer:** D.