Ever since getting my iPhone 6 a month ago, I have incountered a weird feature every once a while, but I haven't been able to reproduce it until yesterday.
I'm posting this because I have earlier been looking around on applevis to see if this has been described, but to my knowledge it hasn't been mentioned. I'm sorry if this already has been discussed.
So what happens is that I will from time to time hear a small sound-effect and the icons of the screen on my iPhone 6 has suddenly slided down, so that the upper line of icons now is somewhere on the middle of the screen, and the corresponding lines of icons below has slided equally down. I also can comfirm this by sight, since the little vision I got left, let's me see that the upper half of the screen now is dark.
After some seconds, I'll then hear the sound again and everything's back to normal.
I've thought from the beginning that this is a new feature so that one can easier reach the icons that are highest up on the screen with a thumb, without having to change position of the phone in your hand, and that's still what I believe this is. But as mentioned above, I haven't been able to reproduce this until now.
So what you do is simply to double-tap the home-button. Not double-press it like the gesture for opening the app-switcher, but a light tap, like double-tapping the screen. I guess this also works on iPhone 6+ and perhaps on 5S, since it probably is the touch ID sensor that reads this gesture.
The screen will slide down and you can reach the highest icons much easier, supposedly with your thumb. When done, you can either double-tap the home-button again to make it slide back, or just wait for a few seconds and it will slide back on it's own.
Hope this might help someone, because it sure made me frustrated to not figure out what caused this to happen every once in a while. And again, if this is old news, I appologize for double-posting this. :)
All the best and take care :)