It's not fine. He knows what's coming next - her chalky skin, the way she lies down nearly as lifeless as a set of hospital sheets. She's going to get close to dying if she's in her own time; here, she'll simply die. And he can tell her none of this, explain nothing about the way that his arms tighten around her when she says it's fine.

"As long as you need," he murmurs, letting her decide when she wants to get up. "We have all the time in the world, Scully."

Patently a lie - but what else can he do? She deserves to have this time. The immortality they joke about should be hers.