You hesitate for a moment. Obviously, it seems like a bad idea to drink something you know will have some effect, but not what that effect is. But then, you reason, if Vivienne just wanted to experiment on you, she didn't have to tell you that these were magic potions at all. She could have just pretended to be some nice old...well, nice young hermit and offered you a drink. A "home-brewed, all-natural drink," or something, it wouldn't have been unbelievable.
So you decide to grab the mug of purple potion. Hope simply takes the coffee. "So, Ms. Vivienne, how long have you lived out here?" she asks.
"Oh, years," Vivienne replies. "Decades, maybe? One of my first attempts at spellcasting backfired a bit, so I've been unable to leave this cabin for quite some time. And since transforming myself into the woman you see before you is...well, trivial, age is no concern. But on the other hand, I've quite lost track of time."
You take a sip of your drink. It's sweet - a bit like white grape juice, but with the consistency of a milkshake. No immediate effect. "That must get a little..."
"Lonely, more than anything," Vivienne states. "Though, fortunately, one of the non-potion-based spells I was able to master is one that can gather ingredients, or other things, for me, so I do have a steady supply. Oh, by the way, Tim, how's the potion?"
"Tastes fine. Not quite like anything I've had before, but it doesn't seem to--eh?" You cut yourself off as you suddenly feel a powerful itch trace its way along your neck, but before you can even reach up to scratch it, your head pitches forward, not only landing in your lap, but rolling forward onto the floor. Hope shrieks.
"H-hey, what the hell?!" you exclaim. You attempt to move your body, but while you do still have feeling in it, you can't move.
Vivienne picks you up and smiles. "Oh, it seems to be working just fine."
"Yeah, okay, great, put me back, please!" you shout, disturbed.
"Aw, but you're so cute!" Vivienne teases. "Plus, there were some sedatives in the potion - that's why you can't move right now, by the way. I was afraid you'd end up breaking something. Or someone."
"No, look, listen, I don't care! This is weird! At least if I'm unconscious, I won't feel it! You, you CAN put me back, right?!"
"Oh, certainly," Vivienne says. "It's only a temporary detachment potion, you'll be reattached to the next surface the base of your neck is pressed against. Like so!" With that, she walks up to your body and...