Aw, thanks! Given that Watson had been looking after a nearly-broken-down Holmes for an unspecified length of time, I figured he had to be deeply, profoundly worn out in many ways.

I also wondered, if speculation that Holmes was trying (again) to kick the drug habit in DEVI is true, whether Holmes might have dosed himself when presented with a case? That, too, might explain his utter stupidity in the experiment - and if you want to take a darker look at it, might also explain Watson's despairing agreement to undertake the ordeal with him...

That all would have taken far too many words to explore, though. ;-)