This issue is now irrelivant. Please close this.

How to reproduce:

Step 1: Do something for a while, Watch YouTube, Play Roblox.

Step 2: Load up Minecraft and create a new world

Expected Result:

Minecraft works normally

Actual Result:

A suspected "Bad Chunks" issue causes the game to be nearly unplayable

Temporary Workaround:

Restart your PC and run Minecraft before doing anything else