Went to log in using a different version and I lost everything except what I was wearing and what was in my inventory.

Went to log in using a different version and I lost everything except what I was wearing and what was in my inventory. Everything reverted to the way it was without any tampering. everything I had done to the world had been erased and I don't know how to get it back. light from torches is in spots where it should be pitch black. i assume its from torches that were there before the world got corrupted.