He'd fallen asleep.
If Crowley had been nearly too exhausted to drive, he'd been by far too exhausted to lean back and will the jeep to drive itself. The first had required only concentration; the second would have needed the sort of resources which, after fighting to will himself warm against the cold cold cold that had seeped in anyway, Crowley simply hadn't got. By the time they'd pulled into the car-park of the tiny inn, there'd been a tremor - a shaky sort of weakness - in his knees and elbows. He'd barely managed to open the heavy jeep door; barely managed to climb the stairs to their little room; barely managed to hold the key steady long enough to unlock the door.
Shrugging off coats, discarding gloves and scarves and sunglasses, and then it had hit them both at the same time, as though it had simply been waiting for the click of their heavy, wooden door, and the rustle of their curtains being drawn: Crowley's breath suddenly uneven, Aziraphael sitting down abruptly on the edge of the bed, and the raw immensity of the time out on the ice all crashing home.
There'd been such need when Aziraphael kissed him (or perhaps when he had kissed the angel; either way), when they'd crawled back towards the pillows, pressed as close as could be. Slow, and intense, and fiercely tender, and in the time it took Aziraphael to extricate himself, flushed and urgent, to pull off his shoes and set the clunky radio alarm, Crowley'd fallen asleep.
(Wearing everything but his coat.)