Have you had contrast before? Sometimes, the contrast (generally and iodine based product) can make some people feel a little "odd", give you a slight flushed feeling or a metallic taste in the mouth. When you get there, ask them to explain everything properly and question them if you have any worries at all, be very accurate with listing medications, allergies, pre-existing conditions and stuff like that. There will most likely be a consent form they ask you to fill out, this is to make sure you are aware of and understand what is going on. Just try and be calm and relaxed, it is a time consuming test, but it really is not unpleasant.