Boredom.
Its black tendrils curl surreptitiously around me, trying to entice me, trying to seduce me, with the promise of having nothing to do and nothing to worry about, with the promise of nothing, absolutely nothing.
And when they have me easily within their grasp they suddenly snap closed, tighten, drag me struggling desperately to the colorless gaping maw at the heart of the deadly creature, its teeth gnashing together in eagerness, waiting to devour my logic and sense and torture me into doing something stupid, something idiotic, because it is feeding on my very self and the only way to injure it is to injure myself as well but it is worth it because this exquisitely torturous affliction of the mind is unbearable and all-consuming and all I can think is that I will do anything to alleviate this terrible tedium, but it has implanted lethargy inside of me and cancelled out reason, leaving me with nothing but idiocy and the knowledge that it is inside of me, and therefore if I hurt myself I will hurt it as well.
And sometimes the creature is weak and I am strong and have too much logic for it, and can force it out without resorting to the crude means it suggests.
And sometimes the creature is strong and I am weak and it easily overpowers my pathetic reason, and I am helpless to its persuasions.
And sometimes, most of the time, we are evenly matched and I curl in on myself in excruciating agony as great and unwinnable wars wage on interminably inside of my head.
I was bored (no, really?) and, in an attempt to alleviate said boredom, began typing about it. As the piece became increasingly darker and slightly less accurate to my own feelings, I realized that while my own boredom may not be this extreme or dangerous, Sherlock's might be. And so this happened.
Also, did you know that spell check does not believe "Sherlock's" is a word? Very odd. Spell check is not very intelligent.