I have a s3 that was working as usual, but the other day I gentle put the phone on a chair when I was working on a computer, nobody sat on the chair but when I picked up the phone to see the time, there was and still is a blackish purpleish...circle thing in the corner of my screen! I can see that part of the screen, but it is incredibly darker than the rest of the screen. the screen is not cracked either, I think its some sort of lighting issue, could someone identify this and help please?