Stop finding excuses for me 
My score for the day was average, leaving me pootling about below 1000. It was actually less stressful because I ignored the time constraints, and made efforts not to berate myself. Laugh at myself yes, but not berate myself... I think it's very useful slowing things down like this and really analysing what is going wrong in my reasoning. It's like learning a "backhand clear" in Badminton. Mine improved a bit after a coach got me to go through my arm motion, very slowly, and then, very slowly, showed me the proper arm motion. I could then see what was wrong with my current "pattern" and then (with practice) play the proper arm motion at full speed. Tactics Trainer is like demanding you move at full speed from the get go. Ok when you reach 1800 level on Tactics Trainer you can see these problems in five seconds, no doubt, 'cause you have already mastered that "backhand clear" and can play it at full speed without thinking.
Slow Tactics Training
Your right, totally right. It's what I mentioned earlier about pattern recognition and it only comes with time and practice. What I mentioned about imagining that the Queen isn't on the board helps with finding a move. As humans, we can't analyse everything as a computer does, so we need those little tricks to help us to spot reasons for making moves - candidate moves. We can then analyse a small subset of what is possible in the position.
I was looking at Caruana Vs Kamsky from yesterday and Caruana's Nxa6. Just imagine Caruana looking at the position and thinking that if the pawn weren't on a6 then he could take on b5 with the Bishop and check. If he plays Nxa6 then, if Kamsky recaptures with the Rook, then Bxb5 will be a fork. It's just a matter of stringing things together from the flight of fancy that he could capture on b5 if the pawn weren't on a6.
Spotting mating patterns will simply come in time and I suspect that your stress of "doing a puzzle" got in the way of solving this one. Deflection plays come from imagining that certain pieces simply aren't on the board. Once you see that the BQ can't leave c8 unguarded then Bxc6 leaps out at you as removing the rook's defender.