For what reasons has Virginia Woolf decided to end her life?

In the Prologue to Michael Cunningham's The Hours, Virginia Woolf has decided to end her life for two reasons. She fears the onset of 'madness' again as she is again hearing voices and she can feel the onset of the headaches associated with her condition. In addition, she feels that she has failed as a writer, seeing herself as 'merely a gifted eccentric' (p. 4).