What's wrong with me?

It began a year or two ago when I suddenly started feeling extremely suicidal. That's all I ever thought about and I could never find away around it. I was terrified that I would kill myself, but even more terrified that I wouldn't.

Now I'm a highschooler and the feeling passed for quite some time. Don't get me wrong, I'm still horribly pessimistic and wouldn't exactly mind if I died, but I don't encourage it.

From time to time I experience such strong urges to kill myself that I have no idea what to do. I simply find a spare room or go outside if none and cry. I don't quite understand why I get these urges. I suppose I hate myself most of the time but I don't get why it comes so randomly.

I don't get it. Am I depressed? Do I need help? Is this normal?