SPOILER ALERT! Hyeonu is definitely not remembering the situation right. It doesn't make sense for his mom to have grabbed the knife if she was comatose. Even if she conveniently woke up as he was about to stab her, there's no way she would have had the strength to stop him. I really hope he didn't actually drink the pill. It's clearly just to control him into integrating into the complex's insanity. Also, the pills are labeled Jimin Ma. I'm guessing that will be his new name if they successfully manipulate him.