I tend to think of the term "Power Exchange" quite literally. When I have a great session and My client is truly submitting, they should feel drained and I should have the energy leaving the session. When I get a client who's just completely shut down, unresponsive to anything I throw at them, too nervous, untrusting, or just without mutual chemistry, etc, that's when I feel drained. Having to pull the vulnerability out and getting someone to submit when they haven't arrived ready to do so is exhausting! I think you've done your job as submissive if you feel completely relaxed, but exhausted, when you leave a session. The feeling you get when you run a marathon --- a feeling of accomplishment--- but worn out! The Domme has your "power" now and you should leave the session feeling like you've given it up!