No. Thinking about suicide is rather common. I read somewhere that one in four people (or something like that) think about suicide at some point. What is uncommon is planning it out in details or think about it obsessively over a longer period of time. That's when you know you should take it seriously. It seems to me that you fall in the second group. So take these thoughts seriously.

I also want to add that depression is not the only mental illness associated with suicide. For instance, people with psychosis might think of suicide more than the average person.