Internal Exception Error

I use a mac air, and it would work great for Minecraft other than the overheating, but after I updated it to v. 1.8 things got complicated. I would get on to a server, and after around 5 minutes I would lag out and then I would get the message:
"Internal Exception: io.netty.handler.timeout.ReadTimeoutException". The problem is that this isn't even an occasional thing its constantly! Every 4 to 5 minutes it'd do the same damn thing. Its very frustrating, and its making it impossible to play.