I've never been able to engage in any medfetting. I just look at pics that I like. Frankly, because of my disability and how many react to it, I haven't done much of anything as far as sexual interaction.
I would imagine that if I ever met a woman who liked my kind of medfet (anything involving the patient wearing an N95 or other protective mask---maybe setting up a medically required fit test or something), I'd likely want to be doing it daily...but then, after several weeks, we both might burn out and need to dial it back. Plus, I feel like I would want to actually write down scenes to go by, which would be time consuming (I imagine some of you do this. Some medplay seems rather complex).
Such scenes might just be some random exam that start with her grabbing a mask to put it on, and wait in the "waiting room", or maybe she is suddenly told by the doctor in the exam room that she needs to wear a mask in public due to some disease they tested for, and is given one and "shown how to wear it properly". Or, because I like certain sports, she could be a runner, and because she is suffering respiratory issues, she needs to henceforth run with a mask on, and she's in for a fit test of possible masks.
Lots of different scenarios, but in any case, I see it trickling down to once weekly at most.