I was playing on my favorite Minecraft world, and all of a sudden, i couldn't place blocks!!!

I was playing on my favorite minecraft world, and for some reason out of nowhere, i could not place blocks!!! If i switched to Creative mode, i could place blocks, put that world was for survival (  I also did not take any damage or couldn't attack')  ( I am very sad please fix this) not found.!!! I really loved that world...