Game hangs up when entering the nether.

*What I expected to happen was...:"
I would enter the nether.

What actually happened was...:
I tried to enter the nether, and after the nether load screen, All was black. No environment rendered, and no sound was present. Game stopped responding when I attempted to exit. Launcher log contained several server messages about lag. Was playing single player.

Steps to Reproduce:
1. Build nether portal (mine was the standard 4x5 box).
2. Enter portal.