Q. A 16 year-old is visiting some friends who are excited about a new drug that they discovered. They tell her it is "natural" so it's "definitely safe." They've tried it before and said it made them feel serene. She has no significant past medical history and isn't on any medications. She decides to try the drug along with them and eventually starts to feel terrible. She feels hot but is surprisingly dry (not sweating), her heart starts to race, her face gets red, she feels "parched" and starts looking around desperately for some water but has trouble articulating the words. One of her friends says the black of her eyes is huge (her pupils appear very wide). Which of the following best explains the pathogenesis of the patient's condition?