"Endogenous depression," he says quietly. Even the words sound sad - limp and self-important. "Long-term major depressive disorder without a clear external factor."

Which is to say, it's just your brain, Mulder. Whirring along like things are fine until there's no crisis to handle, no world to save. He's a wind-up toy walking into a wall, unable to stop until the crank runs out.

"You couldn't take it anymore - and I can't say I couldn't blame you, because I did. But I know it..." He's trying so hard to be fair. "It hasn't been easy for you."