For what little I know about the matter, it is not to abnormal for people to have fantasies in which they are the opposite gender. When I was a high school teacher, I would occasionally deal with it in girls. I have never wished to be anything other than the woman I am. In fact I love being a woman. Yet I know of both men and women who do have opposite gender fantasies. Most of the time it is harmless and in passing. If it does not go beyond that, no harm done. If we desire toact out on them it is another matter and then time to seek competent advice and counsel. In any case it was poor practice for your therapist to snicker at your issue