Why do I think about death?

I noticed lately that I've been thinking a lot about death. I don't want to die, and I'm not suicidal. I just think about what would happen if I died or if someone I loved died. I imagine how sad everyone I know would be. I know it isn't worth it, and I definitely want to live and have a future. I just think about it. When I'm driving, I sometimes imagine what would happen if I just let go of the wheel and kept going.