Is suicide always sinful, even in the case of mental illness?

The glossary contained in the U.S. version of the Catechism of the Catholic Church defines suicide as, “The willful taking of one’s own life; a grievous sin against the fifth commandment. A human person is neither the author nor the supreme arbiter of his life, of which God is sovereign master.”

However, the catechism points out that, “Grave psychological disturbances, anguish, or grave fear of hardship, suffering, or torture can diminish the responsibility of the one committing suicide.” (CCC 2282)