Random Deaths?

So I was playing offline, in the nether and grinding away. I starting stacking blocks to get around a ledge that was above me. Once I hit my head, I built out farther to get past the ledge, then built up once again. I hit my head again, but this time I died. Just randomly. Dead. I was in awe, and I hit return to menu without thinking. It was as if I died from fall damage.