I'm usually good at troubleshooting and diagnostics but I can't seem to find the issue here. When I move my mouse - in any world - it is very hard to control where I am looking. Moving my mouse just a few centimeters causes the player to spin around several times. It makes the game unplayable. This doesn't happen in vanilla.
I saw there was an update available so I downloaded it and I'm still having the problem. I updated less than 30 minutes ago. I've tried adjusting my mouse sensitivity (which was still at the default) and it makes no difference. I'm not sure how much a log will help but here's the most recent one. http://pastebin.com/RC0JFu0B
I'm guessing this is a bug with Forge. However, a week ago or so, I did not this issue. It only started today. I'm currently only using Optifine and I tried it without Optifine as well, same issue.