Well, I'm not so much into the 'blackmail' or 'threat' scenarios because the victim wouldn't be subdued by an anaesthetic in these. I don't just want to give myself up, that doesn't turn me on. I like the idea of being taken forcefully against my will, have to struggle against an unknown assaulter but being finally put slowly under with a narcotic (Chloroform). I just like the idea of not really having a choice. I don't need to care about my actions or decisions because I actually can't make any if I'm sedated.
How about a known abductor? What if, as you slowly lost your understanding of what's going on, you realized you're being chloroformed by someone you actually know, maybe an acquaintance? Would that make you feel more or less helpless? Maybe he has watched you, has noticed your submissive nature and knows you better than you think, thus knowing just how to treat you?