Thats exactly it, right there. See many people don't click that sex actually equals Spiritual EXchange in this realm and its why it can be used to induce out of body states and a whole load of other interesting things if you know what you're doing. Why do you think they call this region of the body a "waist" and that most people waste whats within as they don't have a clue about energy circulation?
Peoples experiences vary but the drunken sailor classed it more as molestation than overt aggression because, quote, "She was sucking the life out of me, repeatedly" and he reported the exact same drained feeling. He reported he felt powerless, was totally seduced and unable to resist. At one point in the convo it clicked that a vampire and succubus may be the same thing but he was already quite old when we met and thus drank himself to death mid experiment.
All because of these nocturnal visits he dared never admit or tell anyone else but spent a lifetime trying to deal with and make sense of what was happening.