I am not trained in that modality but from what I understand Shiatsu is a lot of pressure point holding and stretching, usually with the clothes on. Your therapist could have different variations of that but you can be open with them and tell them what you are comfortable with or not comfortable with. They won't laugh at you, I promise!
Them most important thing about massage is that you relax. Stressing out about what is going to happen in the massage is not going to help that.