DAVINA: “Charge” comes from the Latin “carricare”, to load cargo onto a ship or cart. When you charge a cannon, you load it with gunpowder and shot. Someone who is really excited is charged up, like an overcharged cannon. 
RALPH: Today we often use “charge” in a figurative sense, as the doctor does here. His heart is “charged”, or burdened, with worry. When we charge someone with a crime, we put it on their head. When we charge a price for something, we’ve placed a burden of the debt on the customer.