Of the three stories I have heard like this, two of them ended up involving rohypnol. If you aren't paying attention, it looks like a girl who didn't know her limits. If you are paying attention, it looks like a girl who went from tipsy to sloppy blackout drunk in the space of a Black Russian. The ultimate tell is a crippling hangover. Just be aware - if you ever find yourself far drunker than you feel you should be, there may be an agent responsible other than alcohol.
I'm really certain in this case it was just going too far - I was already slurring-my-words drunk when I took that shot, my inhibitions were generally not lowered (while I did insult the hair of the guy who let me crash immediately upon arrival, I also adamantly and repeatedly confirmed that there would be no bootay-having), and I had almost no hangover. Roofies definitely happen. I try to be cautious about my drinks. As far as I'm aware I've never been drugged... The only other time in my life i've blacked out was definitely due to me not knowing my limits and overindulging. But I have friends who believe they've been roofied. I don't go to that bar.