Game Freeze!

I was playing the game normally and i changed gamemode to survival and i played a little bit then i re-changed the mode to creative. When i tried to kill a cow the cow wasn't moving and i wasn't able to kill it. i tried to write /kill and it didn't do anything.I was not able to use items (sign, clothes, sword, etc.) i was in a flat world so i broke down the bedrock and i fell down and didn't die please help!!!!!