I honestly have to agree with @AnxietyHangover because even if you wait until everyone is asleep you could end up making some kind of noise after being unconscious and alert them to what you're trying to accomplish. If you end up vomiting and making sound doing so that could also raise suspicion or alert someone in your household. It would be best to lie, make up some kind of trip or excuse, and go to a hotel if you can afford it for privacy. Even if you make some noise in a hotel room, no one is going to phone in for a welfare check or security unless you're making a lot of noise.