[ Mulder was joking at first, but now he realizes the Doctor has been completely honest. This man has access to alternate dimensions. He has no way of knowing how they work, but it's clearly affected the Doctor in the worst of ways, so Mulder pulls back on his teasing to try and be more sincere. ]

Yeah, um... sorry. I thought you were insinuating she needed a break.

[ Mulder rubs the back of his head awkwardly. ]

We don't have to talk about it if you don't want to.