Re: clara/lydia.
Yeah, a few of the people here came from a world that has Troubles? Like terrible superpowers or something. And Donna got one, which made her split in two at first. And that was fine, because they were Donna just double your pleasure. But the more stressed she became — her boyfriend disappeared and then she found out what happened to her back in our world — and it just sent those copies making more and more copies. The more stressed they got, the more likely the were to disintegrate.
Oh, that's — completely terrifying, waking up somewhere with a dead body there.