A Secret Fantasy I'm Afraid To Share

I've been struggling with this for years now. My partner is amazing and we have an open relationship where I can explore my kinks, but there's one thing that even talking about makes me feel sick to my stomach, roleplaying as a submissive in a medical setting. It feels wrong because of how vulnerable it would make me feel, yet the idea has never left me. How do other people handle these kinds of fantasies when their partners aren't interested? Am I just supposed to keep it inside forever?