This may be common sense but it may help someone out……
Today I was getting really bad lag, players jumping around, it was very bad etc…
So I reinstalled Unity from here: http://unity3d.com/webplayer/
2) restarted PC
3) Run CC Cleaner and did a clean ( a highly rated freeware computer cleaner)
Now its perfect again, I did have 4 gig of temporary internet files that were cleaned.