Sinking Into the ground

Hi Mojang,
I have a Problem with all Versions since Minecraft 1.8!
When I play Online, I would be kicked or my biggest Problem that I sink nonstop and slowly into the ground. Is this a bug? Must I update Java? Should I deinstall Minecraft and download it again? Please help me, because I can't Play on the 1.8, but all servers change to this version!