That happens to me often in sport mode. If you try to do a sharp 90 degree turn or a sudden U turn at high speed, (say 40 to 50 MPH) you will tilt the drone over on it's side. It's a law of physics

That will take the gimbal to the end of its travel and you get a big bump in the image.
The wind will do this too, but not nearly as much. The wind has done it to me a couple of times, but I don't normally fly when it's windy. (over 20 MPH).
With an iDevice you can tell the attitude of the drone when you're flying by looking at the circle with the arrow on the bottom left corner of the screen. You'll see the inside of the circle is half light and half dark. Its essentially an artificial horizon. When the craft tilts left/right fore/aft, you'll see the horizon tilt too.