After Visiting the Nether and coming back to the overworld, I notice entity lag.

When I go to the NEW nether and return back to the overworld, the entitys in my game start to lag. This did not happen before the nether update. I created a new world thinking that that world was to big, to find that it happened again. ON A BRAND NEW WORLD! When I hit a mob, they seem to float in mid air, pistons are delayed, and pretty much anything that involves redstone or entitys is laggy! And no, this is not my computer.