Which of the following is NOT a symptom of serotonin syndrome?

Vasodilation is not typically recognized as a symptom of serotonin syndrome. Serotonin syndrome is characterized by a combination of symptoms resulting from excessive serotonergic activity in the central nervous system. Common symptoms include headache, sweating, and dizziness, which can occur due to increased serotonin levels affecting various body systems.

Vasodilation, while it may occur in response to certain stimuli or medications, is not a direct symptom of serotonin syndrome. The other options—headache, sweating, and dizziness—are linked to the autonomic instability and neuromuscular hyperactivity that can occur in this syndrome, making them more consistent with the clinical picture observed in affected individuals.