Why do the British POWs send Billy to the hospital shed?

After being captured by the Germans Billy and the other American POWs are housed in a shed occupied by British soldiers. The British are glad to see the Americans, and lay on a lavish welcome for their fellow Allied prisoners, with plenty of food and party favors. They also serenade the new arrivals with a burst of song to make the Americans feel welcome. Later on, the British stage a performance of Cinderella during which Billy starts shrieking hysterically. Billy's seriously unhinged at this point, and it's obvious that he's in need of medical attention. So he's taken over to the hospital shed for treatment. There he's watched over by "poor old" Edgar Darby, who reads to him from The Red Badge of Courage.