Is it normal that i have bad thoughts constantly?

Hi, I'm a 17 year old male from Irelandl. I always think about the worst possibility. At times, when in the car with my brother I would think what it we died, all the possible ways that we could die, what if my brother, my mother, my Grandmother etc. died - how would I feel, what would I do? What if I was to die? How would my family, friends etc feel? It isn't always bad thoughts about death it can be about anything, but this is the one that worries me the most. Is this normal?