A 50 year old man presents to your emergency room in an agitated delirium. He appears anxious, restless, and disoriented. His chief complaint is vomiting and diarrhea. On examination, he is visibly sweating, his pulse is 100, his blood pressure is 140/90, and he has a fever. You notice he has a tremor in his extremities. He has rigidity of the lower extremities. On the neurologic exam, he has hyperreflexia and a bilateral Babinski sign.
You find out that he was at the hospital recently when he was diagnosed with and treated for depression. You ask him about this, and he says, "Oh yes, I read online that St. John's wort is really good for depression."
Challenge: What's the diagnosis?