I've had the screen issue since my 4S on iOS 5. I thought I was the only one to experience it. It's so weird! I have no idea what is causing it. Usually it happens when I try to wake my phone from the home button, it takes longer to respond and than it usually wakes to a super dim screen.
That was the first time it happened for me. It's like the contrast goes too high for a minute or two. And yes it was the same thing - pressing the lock button to use the phone. The guy who works for me also had it happen two or three times.
Bizarre.