S1·E501 Woh Kaun Thi

A man returning from work finds his wife stranded in the middle of nowhere. He gets curious, as she wasn’t supposed to be there. He gets closer and asks if she is okay, but oddly enough, she treats him like a stranger and speaks of a medical emergency. Within moments she disappears into a graveyard and her husband is attacked. After coming back to his senses, he has a spree of hallucinations where he sees his wife appear out of nowhere in random places. What's happening here?