Coma theory time: Sherlock (as the little girl) is on a different plane of consciousness than everyone else, but it’s reversed because we’re in his mind so instead of him being asleep and everyone else awake, he’s awake and everyone else is asleep. He feels alone, scared and powerless. He’s searching for comfort (mummy) or help (looks to the stewardess). There’s outside interference (the phone ringing, could be happening in real life or it could just be John trying to break through to him). He clings to it, but it turns out to be his worst nightmare (Moriarty) rather than the comfort and safety he was seeking.