A mission that meant certain death 

 (Sherlock meta by foxestacado)

Sherlock was prepared to die. He probably planned to overdose on the plane. So when he received an unexpected reprieve from death, he dove straight into cases–working on so many at a time that John tried to rein him in (“you can’t go on spinning plates like this”).

Understandable, really, because Sherlock sacrificed his life for John by murdering Magnussen, entered solitary confinement and accepted a suicide mission. Sherlock thought he would never have this again. 

He worked as if on borrowed time, throwing himself eagerly into situations where he faces death. 

• He tells John he’s “having fun, while I can." 
• When he encounters what he thought was Moriarty’s puzzle, he not only says it’s designed to "tease” and “beguile” him, it’s a “noose” for him to willingly put his neck in. 
• He faces Ajay without back-up, knowing this man has already killed in his pursuit of the Thatcher statues. 
• When snipers attack the house in Morocco, Sherlock leaps into the center of the room to cover John while Mary dove for cover. 
• Perhaps most telling of all, when Mrs. Norbury shoots, he appears to be accepting his fate.

Sherlock thought he was the Merchant of Samarra; he didn’t expect to survive, and anticipated dying throughout The Six Thatchers. He thought these cases were his last.