1. The Cyclist
All that space on the road, and this fella just
happens to bump into John Watson, eh? This would've disorientated John, obviously, and you don't have to be a Doctor to know that hitting your head against concrete can give you concussion.
Going back to the previous point though about the direction in Sherlock, and seeing things through John's distorted viewpoint, Baskerville drugs needn't have been administered to create a hallucinatory sequence, in which John thinks his friend is dead. A knock to the head might be suffice to skew details in this episode, only for the next episode, to clear things up, with the sober re-telling of what
really happened. I mean, how else do you explain a man clearly dead on the pavement after jumping from a tall building? Even if the cyclist has nothing to do with it? If you look at Steven Moffat plot twists, you'd never know exactly how they were solved before the reveal episode. We could only guess that River Song was Melody Pond, when we knew who Melody Pond was; and we only knew that in the reveal episode. We could only guess that the Doctor would save Gallifrey when the means for saving Gallifrey was shown; the means (the paintings) were introduced in that very episode. No, he's not the only writer on the show, but it's rare that Moffat would plant
all the evidence for a reveal in one episode. It's incredibly unlikely that not everything has been explained. The cyclist is just a means to an end - he could've skewed things - but equally, we could've not been shown the whole picture. One of these theories might turn out to be true; they might all turn out to be true. But we've almost certainly not got a full picture of how Sherlock Holmes faked his own death.
How do you think Sherlock did it? Which theory do you favour? Comment below!