Before I found the issue, I was playing on a free map named the International Space Station. To simulate zero gravity, my character would slowly drift upward as if I was in water (bubbles were flashing above my hotbar). When I left and joined one of my worlds, the same effect was in play, either I could not move up/down, or I would float to the sky. This is happening in all my worlds, and I don't want to lose them and start over.