This is a very fun question and thanks for asking it.
For Doc and I it's a bit complicated, sorta kinda but not all that much, lol. Because Doc and I are real medical professionals we do roll play but we roll play by being our true medical selves and or either a younger version of ourselves or as the submissive patient.
For us whoever is the one doing the exam they are the Dom. And whoever is the patient is the sub, naturally. When we play the Dom he plays the doctor and I play the nurse. This is what we do for a living but in play we are a lot more stern than we can be with our real patients, lol. And when we play the patient again we are still ourselves but we are either younger or play a bad patient that needs to have the doctor or nurse put them in their place.
Either or we love both roles because both of us are complete switches. Again after this post I think I need another cold shower. Boy I have been taking a lot of cold showers lately, lol.