While I'm Playing Runescape it keeps Logging me off??!!?

I have a Mac OSX. With the new graphics update the game is starting to really Lag. I've tried changing the Graphic Settings, this does nothing. So while i'm playing I will teleport, Go up a ladder, or just walk and the game will freeze. After like a minute it will log me out and i will be in the lobby. I NEED HELP PLEASE!!