what's the word for the opposite of Christmas?

It was hard for me to realize it, for it was against all I knew before. To me, it had always mattered. It had always been special.
My sister had disappeared, gone away, goodbye, I'll see you on Tuesday, but she never came back, or maybe she was talking about a Tuesday far in the future. My parents were dead, four or five years before my sister went away, just a bunch of memories now.
I sat alone on a bench with people walking in front of me, carrying useless objects they had just bought, Christmas presents or decorations. I was looking at the coloured lights that covered the city, hearing the songs people sang or that came from passing cars, nothing of it mattering anymore. Christmas was not important because it doesn't exist when you're alone. I had no one so I had no Christmas.
And it didn't matter, I kept telling myself.

Two weeks after my sister left, someone knocked on the door. When I opened it, there was only a Christmas card on the floor. Inside it read "Even if you turn off all the lights, the night isn't totally dark". I made a favour to the environment and myself and recycled it.
The calligraphy in that card was my sister's.