Extreme lag on all single player worlds 1.8.3

Every time I create a world or attempted to play an existing world, the game freezes for about 30 seconds before loading the world. Once loaded, I find myself falling through nothing and into the void. After about 5 minutes of this, the world suddenly spawns yet I can't do anything. Break blocks, place items, open a chest/inventory/etc etc. I have been having this issue since 1.8.1. I've tried allocating more memory, redownloading the game after deleting all files. Nothing seems to fix this issue. I would really like to be able to play this game again.