I totally agree with all what the others have said. Just be aware that the Derm may tell you they have students with them, if you feel uncomfortable with this just say so and then it will be just you and the Dermatologist, as sadly you will be standing in just your underwear.
Never allow the Derm to pressure you into rushing through things, In the past i have experienced a Derm who obviously had a pressing engagement and tried to get through his patients at break neck speed.Not clever.
Like P Monkey said ask questions never be afraid to ask about the options open to you, its your body you know it better then anyone

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You will be fine, its just the not knowing that's frightening.
Good Luck and let us know how you got on.
Md