If you open a command block (this also happens with ESC, books, or anything else that "pauses" the game) while you are moving, the screen will start to shake. The faster you are moving when you open it, the more violent the shake is. For example, if you are walking when you open a command block, the screen will shake quite a bit. However, if you are sprint flying and open a command block, the screen will shake very violently. It's very annoying.

How to Re-Create:
-Open a Singleplayer world in the snapshot
-Place a command block and fly a few blocks away from it
-Sprint at the command block and open it