Okay here goes my HC..
Abir falls down and everyone panicks. Kuhu is terrified when she gets to know the truth from Mishti that Abir has been sleeping and the doctor's injection made him behave like this. She feels extremely guilty and blames herself for even thinking of spiking the coffee. But then she's in a fix whether to tell this to everyone coz if she does then she'll lose out on everything she got as a second chance. She repents on being such a bad person and feels horrible. Kunal can't see his bhai suffer and wows to destory the person who did this to him and runs to his bhai. Kuhu is in the garden and she kneels down crying uncontrollably. Just then she feels someone's hand on her shoulder. Thinking it's Kunal she says "Its not me. I didn't do anything" and turns around. It was Mishti. She looks puzzled. Kuhu immediately wipes her tears and asked about Abir's health. Mishti says he's recovering but what happened to her. Kuhu breaks down and spills the beans to Mishti right from Meenu talking about the pills and Abir being her son, etc. She was ready to get chided and slapped by Mishti but she, on the other hand understands (highly impossible in the show).
Mishti now understands that Meenu is behind all this and she's being playing intelligently. She and Kuhu make up a plan to totally ruin Meenu's plan. They tell everyone that Abir is really sick and needs to be moved to the hospital. Meenu loses it and shouts at both the sisters and holds them responsible for Abir's condition. In the spur of the moment she says that the pills were meant for Mishti but silly Kuhu made a blunder. That's when the truth comes out.
Kunal who was a mere spectator until now will express his unhappiness towards his mother and so do everyone else. He takes Kuhu inside. Kuhu apologizes for being carried away with Meenu's words. Kunal makes it clear that his bhai is his world and he can't see anything happen to him. Also it was because of her that he is able to accept Parul maasi and he wants her to acknowledge the fact that Parul is also now important to him. AND then he suggests her staying away from Rajvansh Sadan for few days so she can think clearly about everything and introspect.