Ha ha, fair enough, my friend. We can go multiple routes with this. One that intrigues me is this:
The one laying on the mat was raised with the one giving them the potion, or they are at least very close. They are poor, and the nobility have been taking everything they can from them. In order to bring about their downfall from the inside without arousing suspicion, he was given a potion to make him forget the reason why he went to the capital city in the first place. Now he his back with the one who raised him, and the part of him that held the motive is going to wake up when he drinks the potion now. What the other man does not know, is that the one who went to the castle made friends and lived a happy life (all things considered) and may not want to destroy the nobility now.