Whenever I go into any server or single player game, minecraft decides to flash and show numbers. The best way I can describe it as, it's having a seizure.

(Also, it doesn't matter what release I'm on, it just happens. I tried changing the release, thinking that was the problem, but it isn't.) When I look at other people their skins turn to numbers and the flash quickly. After about 2 minutes it gives up and crashes. I've logged out of minecraft, restarted it and my computer, but nothing will work. I'm not sure what to do about this. It seems no one else is experiencing this. I have a mac, if that's any useful information. Please reply ASAP as I really can't do anything on it anymore. I made a copy profile, and that didn't help either.