It's definitely the sleep button. I'm concerned as the button went on my 4 and I had to use the paper trick to get it to work.
Yeah they all have the issue. I've had 3 5s's and they all do it. Everyone that doesn't have the 5s says it's the camera lense but it's not. If they had the 5s they would know. They should probably quit responding with that answer until they get the phone themselves.