During these long winter nights, you might find yourself visited by dead relatives.
Even if you can barely recall their faces, they can appear in dazzling, hi-def detail while you sleep. You might dream about your father in his mustard-yellow alpaca cardigan, or even detect the clove scent of his aftershave and hear his gravelly voice telling you to dump your girlfriend.
"The brain definitely has this amazing capacity to create an entirely lifelike experiential reality in our dreams," said Kelly Bulkeley, former president of the International Association for the Study of Dreams in Berkeley, Calif.
What's more, dreams seem to run on a subconscious calendar.
Even after the holidays, people from the past can rise from the depths, reeled in by thin threads tied to traditional family gatherings.
"There definitely is a circumstantial trigger," Bulkeley said. "This is what dreams do. They keep us connected to our roots as they try to imagine where our future lies."
The study of dreams dates back centuries. Aristotle believed them to be demonic. Freud interpreted them as a glimpse into the unconscious. One of the first quantitative studies was done by Mary Whiton Calkins, a psychologist at Wellesley College in the early 1900s.
But with the help of new technology, dream research has been advancing dramatically, said Bulkeley, one of the small cadre of researchers who collect data from computerized "dream banks."