I told two Mistresses that I have served over the years that I was in "deep subspace." And I was. Neither discussed the subject directly.
For the first one, a mature Mistress, mentioned her "alter ego" taking over in session and I knew exactly what she meant. She was always reserved and, even in phone calls or outside of sessions, she was in control of me.
To a lesser extent a Mistress I knew for a long time, who was a few years her junior, was always in control. As I evolved with her and accepted (relished) more and more fetishes and went deeper into "subspace" you could tell she was turned on by it more and more.
There was a possibility of an actual relationship with one of the Mistresses... maybe both but I am not sure. The bottom line is in both cases I would have to remain a sub, in real life outside of sessions. As I said in another post about such matters, that's an impossible situation. At least for me.