In abnormal psychology, I read/heard that most people have passing thoughts of it. But they become abnormal when it occurs frequently, even if there is no will to act on them. I would say that sounds about right. I think most people have thought about it at least once just in passing. Those of us who think about it frequently, however, typically qualify for a diagnosis of depression, bipolar disorder, or another psychological disorder. Therefore, the thoughts could be symptoms of the disorder. If I remember right, the thoughts with no intent on acting on them is suicidal ideation.