"I would have said you were investigating, but I wouldn't use my terms for your line of work." It's a dismissive tone. Like a banker talking to his cabbie. "But therapy to cure a virus. If only all neurological diseases worked this way."

There's no other explanation; even here, Sherlock falls back on the supernatural as a last resort. Even if this was some plague upon them, the effects were just as physiological as the common cold. Still, he honestly can't help the little jabs, cutting all the red wires attached to Jim's fuse for as long as he could. He's entitled to it. To everything, after what's been done to him.

"And fit as a fiddle, you are." Considering the prerequisites, entirely unsurprising. "Shame."