Fear in the Night (1947)

Bank teller Vince Grayson wakes from a nightmare in which he and an unknown woman murdered a man in a strange, mirrored room. Only a dream...but Vince finds that he has physical objects and bruises from his "dream." His cop brother-in-law dismisses his story...until the family, on a picnic, takes shelter from a thunderstorm in a deserted mansion containing that mirrored room. Is doom closing in on Vince?