That's how Simon & Garfunkel referred to this time of year in the Song "I Am a Rock".
Leonard Cohen also referred to this time in his Song "Famous Blue Raincoat": "It's four in the morning, the end of December..."
Perhaps this Time of the Year is Utilized by the Poets because of the Thoughts and Emotions Evoked. Christmas is over, the New Year has not yet begun, so these are Days of Reflection and Anticipation.
I guess "Deep and Dark" could easily be taken as being Depressing, as we are Deeply in the Dark of the Winter Solstice.
But Hey- there's always the Thermostat and the Light Switch! That's Something Positive!
As I understand, Sabby has had Positive Results with Joey. Good for you both!
Here's Hoping Everyone's "Deep and Dark December" is a Positive Time of Reflection and Anticipation!