Well, what a mess. I'm sorry you've had this experience, OP. I've been in similar pickles myself in my youth, and I've been in that dark place you're currently inhabiting. It ain't pretty
A couple of things: you say you vaguely remember having sex. My guess is that it was a fumbled, drunken episode on both sides, and I really see no reason to tell your husband. None at all. You weren't having an affair. You probably wouldn't recognise this man if he passed you in the street. What's to tell? What's to admit? The truth rarely comes out in alcohol ... just your inner eejit. Best kept under wraps, imo.
Of course, it's possible that your drink was spiked. But I come from the generation before this phenomena took hold, and I was just as capable of getting myself into this type of mess twenty years ago, on drink alone. I think it's more likely that you were just incredibly drunk. It was a quiet pub on a Sunday night, and you've admitted to flirting. That's fine, and it's nowt that hasn't happened to many women before you. It went wrong, but it could have been much worse, as you've already acknowledged.
I agree with all the advice about the MAP.
Lastly, the barman won't be inclined to help you out here. If you walked into the pub obviously drunk, he should not have served you. I work behind a bar, and there is no way I would serve a person who was already clearly inebriated, not least because it's illegal to do so.
Any how, please don't dwell any longer than necessary on this incident. You were very drunk. Give yourself time to mend, and move on.
Oh .. and NEVER drink brandy after wine!!