The holidays are pretty stressful for a lot of people, what with the traveling and the buying of gifts for little cousins and parents that don't like anything and all of the needing to be happy all the time because it's the holidays and you're celebrating various things, or possibly nothing. (Which is stressful too, arguably more so.)
So you're just a basket of nerves, and making the situation all the more, uh, interesting is that some recent research suggests that your stress-hell makes you more likely to hallucinate.
Maybe you've heard of the "White Christmas" hallucination tests before. They've been going on since Barber and Calverey’s landmark 1964 study examining the degree of clarity with which participants in a silent room could imagine the Bing Crosby song in their head. It helped establish a standard for "normal hallucinations," i.e. that one might hallucinate and not be mentally ill.
A 2000 study by Harald Merckelbach and Vincent van de Ven added an additional element: participants were given, instead of silence, white noise. They were asked to press a button if they were able to hear the song "White Christmas" within the noise. But the song was never actually played. Despite that, a significant number of participants pushed the button, suggesting a hallucinatory experience.