Mulder's not tired, but he knows when Scully is - nearly before she starts yawning. And they both know about the dangers outside his door. It leaves them with limited options, just like Dana "I'm going to make you sleep if it kills me" Scully probably wanted.

"Probably too late to catch a cab," he says, glancing out the window. Does this place have cabs? Not that it'd help, if the driver ended up infected with the curse. "Look, you take the bed - I can go into the other room."

'Bed' in a manner of speaking, anyway. He'll just flick the lights out on here, and maybe he can sit on a different floor, see if it changes his mind about feeling drowsy.