I think there's two questions there: 1)Do people who kill themselves do so without warning, and 2) Do people who kill themselves without warning have form for trying to kill themselves.Do people usually take their own life out of nowhere or have there usually been numerous attempts/thoughts of suicide, leading up to it?
The answer according to recent research is yes to both. Only 1.6% of people who kill themselves had warned of their imminent suicide beforehand. The rest told no-one. 65% of perpetual self harmers eventually complete suicide.
Go figure.