I opened my game and I'm stuck on the Y level I saved at - can't go up or down stairs, and I can fly out the door despite playing on Survival. It is also showing the swimming bubbles, but I seem not to run out of air. 

so... I just started flying around to kill time and I ran into a waterfall on the side of a mountain, half hoping it would drag me down but instead it has propelled me up - my Y coordinate keeps rising without me doing anything - I can only control X and Z.