I think that it is "normal" to have a plan in the back of your head if you have felt suicidal before, which most bipolar people have. So, I think it's normal for a bipolar person.

I'm doing really well right now, no suicidality or other depressive symptoms, but I still know what I would do if I needed to end my life, because I have made these plans before. It's the simple result of having a memory.