I mean there isn't enough in the thing to really analyze what might have actually happened. Tons of possibilities here, but I will say this, I don't think the pill or whatever it was on the table was a roofie. I highly doubt that Hilary is stupid enough to leave something like that out on the table where Pip, being the pervert he is, wouldn't know what it was. Still, if he was roofie'd I am curious if Hilary is actually showing another side of her personality that we've seen before. Her possessiveness.
She was jealous because Kat had something she had before, so the immediate question here is does she view Pip in the same manner? Could it be possible that it was kind of a baiting tactic so she can grab Pip and lock him up somewhere so that they can 'be together forever and ever' sorta deal? I'm not putting my money anywhere, but I think just her doing it to be vindictive to Kat is rather....silly. After all, Kat doesn't really like Pip. Which is rather apparent. Unless we get a situation where it becomes...."You can't have him, he is mine sorta deal." which Kat counters with: "Keep him, didn't want him anyway." Leaving Hilary embarrassed and speechless at the fact she nailed Pip and did a bunch of things with him that literally resulted in only slight discomfort from Kat. -Shrugs- Or maybe she is setting up for a legal battle or who knows what. Really I would like to think that Pip just conked out from over-welcome and some over-consumption. I don't think her personality has changed that much, but it would be nice to see an arc that added Hilary as a more sympathetic character. Sure, everyone needs a villain, but Hilary is vastly unexplored and doesn't really have any motivation for her actions aside from well...being a bitch at times. (Chaotic Evil?)
Regardless, we've already had plots with the shadow thing and other villains. At this point Kat should kinda be rolling her eyes and shrugging her shoulders going. "This is a minor annoyance, but you're not trying to kill me so, all is good."