Why does Catherine starve herself, in Wuthering Heights?

When Catherine confronted Heathcliff about the latter's embrace with Isabella, Healthcliff told Catherine that she had no right to be jealous. Edgar then confronted both Heathcliff and Catherine. He told Catherine to choose between him and Heathcliff. Instead of answering, Catherine locked herself inside the room and refused to eat for three days. She was also upset because Edgar stayed away from her.