Which of the following is a symptom of Serotonin Syndrome?

B is identified as a symptom of Serotonin Syndrome because this condition is characterized by a combination of physical and mental symptoms resulting from excessive serotonin levels in the brain. An altered mental state, which can manifest as confusion, agitation, or hallucinations, is a clear indicator of this syndrome. Sweating is another common symptom, as the autonomic nervous system is often affected, leading to increased perspiration.

The other options, while they may present in different contexts or conditions, do not specifically align with the hallmark symptoms of Serotonin Syndrome. Euphoria and increased energy could occur with certain mental health conditions or as side effects of stimulant use, but they are not diagnostic indicators of Serotonin Syndrome. Loss of appetite and weight loss may occur due to various factors, including anxiety or other medical conditions, but they do not directly represent the syndrome. Fatigue and weakness can relate to numerous health issues but are not specific to the presence of serotonin excess in the system. Thus, altered mental state and sweating best encapsulate the signs of this serious condition.