What are some quotes or even preferably a passage that shows Oswald Alving is mentally ill?

The son of Captain and Mrs. Alving—and, as it is revealed, Regina's half-brother. Osvald is a painter in Paris, where he delights in "the joy of life." However, he has been sick and cannot work, and, now back in Norway, he tells his mother that the doctor said he has been "worm-eaten" since birth. He decides that it was his own lifestyle that caused this, but eventually, Mrs. Alving tells him the truth about his father, whom he once saw as a paragon of perfection. Osvald does not want to live in a vegetative state and had planned to have Regina take care of him when the time came, but he turns to his mother at the end of the play to give him morphine tablets. As the sun comes up, Osvald's brain breaks and he begins to slip away. He is last seen muttering "the sun" over and over again.