I hesitate to write this because it sounds off. But sometimes, I try to turn off my excessive analytical thinking and put myself into... I don't know what to call it. "Trancelike" is what I'm going to use, but it's wrong. There's no word for it.
It's like, the mind is hit with a flow of thoughts and impulses. I'm sure your mind works at least a little differently than my own, but I often start analyzing and deconstructing all the thoughts, analyzing, thinking, pondering.
Sometimes I want that to go away. Drugs can do that -- I've done it with both recreational and performance drugs in times past -- but that's not what I'm talking about.
Even over and beyond that, I think a lot of drug use is a placebo.
I use "drug" broadly -- slammed a couple energy drinks in a row, lots of coffee, or liquor all can be used partially to induce this sort of work. But the chemical effects of these substances shouldn't take effect for at least a while as they metabolize. Slamming two big energy drinks in a row shouldn't have a dramatic effect on your consciousness, beyond just letting you make your own mental associations with the energy-drink-emboldened state of mind.
Loud music in headphones is my go-to lately, but truly letting go and just letting action come without judgment, hesitation, or analysis is not at all assured. Physical fitness beforehand -- intense cardio or strength training -- seems to help.
Some other things help. Being exhausted is a mixed bag; sometimes it can help.
For music, usually but not always something electronic that just kind of blends into the background.
This one I've put on lately is fine -- http://www.youtube.com/watch?v=vg_yl9Ctq6Q -- not incredible or anything, but it gets the job done.
Then, I don't know when or why it happens sometimes, and not others. Sometimes I'll stop analyzing/thinking and just work at a prolific pace without introspection, hesitation, or analysis. Trancelike, sort of. Not a trance. It's hard to describe. It is interesting, though. And sometimes results in a prodiguous output of good work.