When in the Nether, I tried to build up multiple times to try to reach a new level of the land. As I was build straight up, I had started taking fall damage when I wasn't falling from anywhere. It would also get to the point where I would end up dying from fall damage when I didn't fall and I was still building up. I don't know if this happens to other people but it has occurred multiple times when I have been in the nether.