When it's voluntary-I am giving up power to him, in a sexual situation-it's an amazing rush. I don't have to be responsible for running things, for keeping things going like I do in r/l. I am relaxed and energized at the same time, and I get full body shivers. Even though I have and would only submit to someone I trusted completely, there is still a tingle of, not fear exactly, but knowing that I have given him permission for, basically. It feels dangerous and totally safe at the same time.
To try to explain by example: lover/Master and I were together, in bed, very vanilla, and I was complaining, sort of wistfully-not a full-on bitching, you know?-that we didn't have any toys with us, to take the play up a level. The room was dim, but not dark, so I could see his face, his eyes. I am not into breath play-fine for others, just doesn't do anything for me. But l/M took his thumb and forefingers (or maybe first two fingers, I got kind of lost in the moment,) and grasped my Adam's apple. He used just enough pressure that it was firm, but came nowhere near cutting or even shorting my air supply, and looked into my eyes. I knew that he could, with just a little more pressure, take away my air, and with a little more, could have crushed my windpipe completely. I knew by the look in his eyes that he knew it, too, and was checking to make sure I knew. "Normal" people react to a threat like that by bringing chin to chest, to protect the area, but I lifted my chin, giving him greater access. Why? Because I also knew that he wouldn't do it-no breath play is a hard limit for me, and I knew he wouldn't cross that line. But feeling his strength, not just physical, but the strength of his power over me, well, if I had been vertical, my knees would have given out, and he would have had to catch. And he would have, then held me till he was sure I was okay, physically, mentally, and emotionally. I realized, and this did scare me a little, that he could have squeezed-hard enough to do damage-and I still would have left my throat exposed for him.
We don't do TPE; BDSM is a bedroom game for us, although we have talked about playing for a whole weekend, staying in role the whole time. But when we leave the bedroom (or bathroom, or living room, . . . ) Okay, to rephrase: when we leave the situation, we are equals, which means that I am better, stronger in some areas, and he defers to me; and he is better, stronger in others, so I defer to him. We respect each other as independent people. I don't want to live 24/7, but that sexual power of his is always there for me. I don't know if he understands how deep it goes; or maybe he does, and that is why he has been pulling away lately. There is a song by Evanescence called "Good Enough," and one line stands out for me: Be careful what you ask of me, 'cause I can't say no to you. I don't want him to run my mundane life; I am okay with the fact that he can evoke sexual, often submissive feeling from me at his will.
I hope that helps your book/writing. Good luck!