1. ?wear off
The drugs effect was wearing off and that reminded him the pain of his broken leg.
2. ?feeble
The old lady lying on the bed was too feeble to ask for a cup of water for herself.
summary:
Harry and Ron had driven the flying car for hours, so they were not as excited as the beginning. They were so thirsty that they wanted to sit in the train and drink sone icy juice. The worse thing that the engine seemed to have some strange sound happened to them. They hoped the trip would end soon.