“I began to draw an invisible boundary between myself and other people. No matter who I was dealing with. I maintained a set distance, carefully monitoring the person’s attitude so that they wouldn’t get any closer.” — Haruki Murakami
Actually, Mycroft wasn’t alone on Christmas Eve in a big, cold, void house, staring into the flames of his fireplace in a dark lonely room like a sort of modern Dickens’ Redlaw because he IS a lonely person, who has no significant others in his life.
He just had a slight headache and needed the quiet of a dark and peaceful room in order to escape for a few moments from the merry noises made by his wife and his seven children, all very excited for the festivity.