Are suicidal thought really abnormal?

There are times that I just really feel like cashing it all in, memories flood my mind and I literally hurt.
If it weren't such a permanent thing to do, it would by more tempting, just to get away from
the thoughts that follow me.
I tell myself to keep going, that most people get discouraged, that I need to "man up" and not be a wimp.
So, how common are thoughts of this nature?