I haven't played minecraft in a couple months, a couple days ago my friends wanted to play so I joined their private server and I've been having this problem.
Its not just on their server, it does the same thing on all servers. I will be playing with normal frame rates and good game play until everything goes unresponsive, mobs stop moving, blocks don't drop when they break. And then I lag out of the server.
I have tried with and without Optifine, and with different resource packs. I'm playing on version 1.8.3 but it still does it in others. The error I get when I lag out is:
Internal Exception: java.io.IOException: An existing connection was forcibly closed by the remote host.