As a switch I see this as two questions. My BDSM nature is something I can't turn off: I tried for a while in my first marriage and wrecked my head. Of course I don't express it in everyday life, any more than vanilla people just fuck in the middle of the workplace, but it's always there: if someone gives a Dom or sub flirt I'll respond in kind.
On the other hand, which side I express is something I can choose. At one time I essentially shut down my Dom side for a couple of years (long story), which just meant that I got a lot more interested in sub fantasies: but when a situation arose where I felt it was OK to be Dom, it was all there just waiting to be let out.
Dom is my default state, but if someone attractive comes on dominant to me I can decide whether to indicate by word or deed that I'll only play if sie submits, or to let my sub side respond. (I've had some entertaining duels of flirtation with Dommes trying to tease a sub response from each other.) And I can imagine the possibility, though it's not happened yet, that I might meet such an irresistible Dom(me) that I'd submit without the choice.