You have to look at the interviewer and see them as a person, sure they represent the school, but they themselves are a normal people with families and hobbies. The school already thinks you might have what it takes academically, now they are just seeing if your not socially inept. Which a lot of our fellow science majors are by the way. You're never NOT going to be nervous, but you don't have to be a weirdo. And a lot of these "interviews" are more like conversations than being drilled with questions. Reading the SDN interview feedback section and being over prepared will also ease the stress. Good luck!