Ups nasty question! How to reply on that so it's understandable and then in foreign language... Well I'll give it my best shot.
First there of course is the control. I've got this girl, all tied up and helpless. I can do what ever I want to her. She is totally in my power and mercy. I know that I'll have to control yourself and stay inside the limitations.
Next I feel pride, love and thrust. Not to mention very honoured. Knowing that she love and thrust me enough to le me put her in this helpless situation and know that I wont harm her.