If you haven't gone yet, I just had mine done today and it's still fresh in my mind. If your teeth are sensitive you will feel it. What I figured out half way thru the process was that her instrument pulling back on the gum was more painful than the scaling/planing. All I got was a gel solution to numb. Request novacane injection and you won't feel a thing after the needle. Smile.
Scaling and root planing can be rather uncomfortable from my experience. This is something that is done once in a great while if there is some tartar build-up along and just under the gum line in areas where a toothbrush and floss do not fully cover. Sometimes if you are new to a dentist he or she will have you go through this to bring you up to his or her standards. Dentists, of course, do not use the term "pain", but call it "discomfort". You might inquire if it would be wise to take an acetaminophen, ibuprofen, aspirin, or some other OTC pain reliever before heading to the appointment.