I would go there expecting a pleasant and civilized chat with somebody who will undoubtably be a very experienced health professional in that particular field.
These type of consultations are not designed to be an obstacle to progress, but are meant to advance and facilitate the process wherever possible. There are a great many conditions where further investigation or information is required because of a past or current medical problem. Obviously the intention is to ensure that any past or present condition or treatment is compatible with the patients excercise of a medical certificate.
I understand your apprehension, but I believe the consulation will be a very relaxed and worthwhile experience. Obviously it is necessary, but you are likely to come away with a very positive opinion of the experience. The consultant will be very experienced in whatever problems and treatments you will be discussing, and again you must remember they are looking for a positive result as much as you are.