This is not a man who you want to have a lot of time on his hands. To escape this boredom, he turns to hard drugs. Watson, played by Martin Freeman, has to literally drag him out of a drug den in "His Last Vow" and most of "The Abominable Bride" is set inside his drug-addled mind.
New Line Cinema
The weirdest part of his dream is when he's an evil dragon and Watson is a Hobbit.
This isn't a man who's naturally inclined to help the police solve a basic, run-of-the-mill murder. This is a man who is a day away from killing himself with an overdose.
Fortunately for Sherlock, he has a brother who cares for him. Mycroft -- the smarter, more successful sibling -- has obviously known about his brother's heroin addiction for a long time, to the point that he recognizes subtle signs that Sherlock might be about to relapse. Mycroft also knows that, left to his own devices, his brother's smack habit would be the death of him. This is why he sets up incredibly complicated crimes for Sherlock to solve, a la The Game.
First, Mycroft hired an actor named John Watson.