What is the change in the main character's demeanor in the chapter and why?

The main character starts out calm and even tempered in the morning when he is admitted. But in the afternoon he takes a nap and when he wakes up he suddenly becomes agitated and angry. his nurses find that he's sitting on the floor and they cannot calm him down. His demeanor changed because when he woke up he came to believe that his leg was not his own, that it was someone else's. He wants to detach it and find his own leg but cannot figure out how.