In this scene, Paul is riding in a train car with two bunk beds. His friend Albert Kropp is put on the lower bunk, and Paul takes the top. At first he is amazed, to the point of not wanting to get into the bunk at all. It is covered with pristine white sheets, and Paul's clothes are horribly dirty—he also has lice. The sister, however, insists that he get into bed anyway. With her encouragement, Paul gets into bed and pulls up the covers. A little while later, the train begins moving.
When he wakes up, Paul realizes he needs to use the latrine. As he tries to descend the ladder of his bunk, while the train is moving, his foot slips and he tumbles to the floor. Remember that he also has a cast on his leg, which makes movement more difficult. So, hitting on the floor with a curse, Paul finds himself flat on his back. He complains of his head hurting, but when the sister comes in to check, she finds no fever. Though Paul is too shy to explain that he needed the latrine, Albert comes to his rescue and manages to communicate Paul's need to the sister. Ever efficient, she brings a bottle, and Paul uses that—no more falling out of top bunks due to his cast and the call of nature.