I understand this. I wouldn't label it as SI. When I try to think back, I remember wishing this when I was as young as 10, and I only started having very suicidal thoughts 2 or 3 years later.

I would bring it up to your doctor and discuss it, but I wouldn't worry much about it. I think more than anything, hoping you'll die in your sleep is a bit of a 'coping' method for us depressives.