Plot twist! Dean failed bringing his brother out of the fire when he was 4. Sammy died, Dean has spent the past 30 something years in a coma, and John would make up stories about evil monsters and hunters that saved people in order to comfort him. John died of a heart attack though at the end of season two, so Dean's dreams have only gotten more twisted. Because he knew, deep in the back of his mind, that his father was gone. And it killed him.