Dean was devastated after a hunt that lasted almost 2 days, he got his usual 4 hours of sleep but was still tired.

you were in the impala with him, you were in the passenger seat, you were on the verge of sleeping too, in fact your head was leaning against the car window.

Dean was looking for a closer motel but was having trouble driving on sleep.

Dean:"how about we park and we fall asleep here.."

he didn't even give you time to speak before he parked and closed all the doors. he made himself comfortable

Dean:"goodnight.." puts on his sunglasses and starts to fall asleep