Su Mu did not faint, was not drugged, nor was she knocked out; she was simply threatened by Xu Yansu. If she didn't obediently comply, the syringe that Xu Yansu held could be jabbed into her skin at any moment, making her end up like the old lady.
In the past, Su Mu was not afraid of death, but after having Su Yimo, her fear grew. Without a father, there was no way she could be without a mother as well. Su Mu couldn't become a burden on her daughter, so she had no choice but to submit to Xu Yansu's threats and obediently follow her to this unfamiliar place.
At that moment, Su Mu was the only one in the room, tied to a chair, her hands bound to the armrests, immobilized. The room was so dimly lit she couldn't see her surroundings clearly. The air smelled of various materials burned by a great fire. She suddenly remembered that Xu Yansu had mentioned a research institute burning down while they were taking wedding photos–perhaps this was the institute Xu Yansu had mentioned.