Which of the following symptoms is characteristic of a seizure rather than a syncopal episode?

The characteristic symptom that distinguishes a seizure from a syncopal episode is the presence of involuntary muscle contractions. During a seizure, especially in generalized tonic-clonic seizures, individuals may exhibit rhythmic muscle contractions and convulsions, which are caused by abnormal electrical activity in the brain.

In contrast, during a syncopal episode, which is often related to a temporary decrease in blood flow to the brain, there is typically a quick loss of consciousness followed by a spontaneous recovery. However, muscle contractions would not usually be present unless the syncopal episode was prolonged and resulted in a secondary seizure. Thus, the key distinguishing feature is that involuntary muscle contractions are specifically associated with seizures.