A patient is brought to the emergency department. he is restless, has dilated pupils, is sweating, has a runny nose and tearing eyes, and complains of muscle and joint pains. his girlfriend thinks he has the flu, but she became concerned when his temperature went up to 103° f (39.4 ° c). she admits that he has been a heavy drug user, but he has been trying to stop on his own. the nurse suspects that the patient is experiencing withdrawal symptoms from which substance