Currently the world is treating me like I am underwater (bubbles above hunger bar, moving slow, mining slow), but I cannot move vertically.  I can technically fly, but moving into stairs does not let me move up or down.

Warning to people experiencing the same thing: DO NOT ride a waterfall down as you will keep going down, and when you hit land and try to jump you will keep going up.  I am currently stuck at Y 254 after exiting and re-entering.