I had purely sexual fantasies once about a therapist that was not associated with romantic thoughts in any form. It was very obviously transference, triggered by a specific event, and lasted just two days. I told him about it and it was very weird because when I was there, looking at him, speaking to him, I very clearly and intensely felt that my fantasies had nothing to do with him at all and I did not find him appealing at all, even the opposite a bit... But it was interesting how those feelings and fantasies surfaced, what triggered them, the content, etc. He seemed pretty comfortable discussing it but we only did once as the whole thing vanished from my mind and never came back after.