spilt/frozen screen

Has anyone encountered a similar problem and can offer some advice on how serious this is. I've run disc utility and it is saying all is OK. I know the battery is going to need replacement some time in the next couple of months but i haven't has the warning yet. Basically out of nowhere the screen did this. I then restarted and it happened again so twice in 24 hours. All ok now but can't explain it and can't lose the mac due to uni pressures!!

The pic is the full screen and it's a 2011 15" Mac Book Pro