The Doctor was rather more familiar with that desperate squeak than he'd care to admit, and he immediately took pity on the human man in front of him. "It doesn't work like that," he said, gently. "When I open the watch, you go back into me. You don't die. Not really. Not the way you're imagining. Not that we need to be terribly worried about that just now. You're not here because of the watch."
How was he supposed to explain what was going on, he wondered, when he didn't truly know himself? He supposed the straightforward approach would be best. John was, after all, a part of him, which meant that he was rather bright. "You know where this is, don't you?" the Doctor asked. "You remember, from your dreams."