I think the easiest and most affective road to take is honesty. We are so used to being judged by others for how we feel that we've learned to hide our feeling to make our lives simpler by not having to try to explain we "just feel-----", fill in the blank, to end the questions we have no answers for.
Just tell the truth. This is a doctor. A trained professional who is there to help you. Best of luck with your appointment and don't beat yourself up if you cancel the first one