A closed Door

Last night we went to bed as normal leaving open the door to the hall and the one into out bathroom leading off the bedroom.  During the night I got up and as it was pitch dark made my way to the bathroom - I banged into the closed door!  There was no wind and the door had definitely been open when we went to bed.  we leave the door open every night - our dog who sleeps on our bed has a water bowl there and if the door had blown closed she would have made a fuss - she even barks if a cat walks past the house!  So what happened - is  our ghost at work again!