@bocaholly - I hesitate to post this on the forum - it will be seen as "so wrong" by many players LOLOL - however - let me write about how it seems to me....

I don't (can't) play anything that cleanly at that speed (yet).  But I DO get a sense of what's happening (for me) in some of the tunes I can play fast.

It's a strange, almost zen-like if you get the analogy, state of playing without playing.

I have no tutor - but for starters I have to agree - play it slow, and importantly really, really cleanly and precise - timing, fingering, clean string crossings.  Get that bowing rhythm totally nailed - but let if EVOLVE to how you "feel" the tune.  For most fiddle tunes, simple sheet is but a guide, a suggestion. [ to me, that is - that's not a generic statement ]

When I start out on a new-to-me tune I will use sheet until I have it in  my head - the sheet (for me) then has to go.  I will take what the sheet has "suggested" both for tune and any embellishments and bow-direction changes etc, and modify them if necessary to get something TOTALLY repeatable - this takes a goodly number of play throughs and patience - and I'm STILL playing relatively slowly, paying attention to everything.

It's almost sensory overload - you're processing so may variables at once... 

Then gradually, just as I earlier discarded the sheet, I discard the "thought processes" (like accentuate HERE, make that SECOND triplet work on an up-down-up bowing-jiggle and not the down-up-down I had to use on the first earlier triplet to get the bow direction back to what I want, like REMEMBER to make that little 4-note run a flying-staccato and not slurred - and probably not what was indicated on the sheet I have now lost anyway, like remember just when I want to change bowing lanes and or change dynamics ) 

By then I have also long-since stopped thinking about the actual notes to play - they have become automatic...   the notes have no name in my mind...  eventually it ALL becomes wholly performed on auto-pilot.

And to return to my curious comment - if "normal playing" involves continually thinking about the notes, having the brain consciously multi-task by following sheet, actively thinking about all these earlier things I mentioned, then sure - you are "playing" and indeed, playing by a set of conscious rules and a thought-about sequence of operations.   

However, once you're in this autopilot / zen-like / trance-like mode - you are in this "playing without playing" mode - I know it sounds utterly crazy, but that's just exactly what it feels like to me......

And it's not just for fast pieces - for naturally slower pieces - in that state of playing you can automatically transfer the "feeling" you have in the moment directly into the dynamics of the piece - you have no other conscious thought process going on and you can put EVERYTHING at a conscious level into the dynamics - it is hugely satisfying....  

Disclaimer - I am not suggesting the ideas in my approach are in any way suitable for others - I was merely attempting to describe how this transition to "playing without playing" happens for me (on some of my tunes - each one has to be worked on to the same degree to get to that state- so - sure - I have MANY tunes that simply don't merit the effort, and on these - I'll "fail" sometimes - why - because I'm thinking too hard and haven't taken these extra steps and time.... )

Again (to my mind) many disciplines can fall into either the arts or the sciences - a common split.   My personal background is one of science and engineering - and oddly I see math and physics in almost everything to do with the violin - perhaps what I was trying to say about it in that ramble is that if you're just "playing" - that is - "thinking (i.e analyzing and correcting in real-time)" about what you are doing - then your are in the "maths/physics" category (even if you know nothing about the subjects).  But once you have decoupled all that cr4p from your foreground consciousness and it becomes sub-conscious - it becomes an art form - my "playing without playing".   I see this in most of the truly great violinists - to my mind they are quite clearly elevated to a different plane of consciousness (or is it sub-consciousness).   I'll never be in that league - but the occasional attainment of such a state is truly rewarding.

Hahaha - bet there'll be a few TL:DR comments !  

Indeed @bocaholly - "internalization" largely sums it up, and I like the golfing analogy.  And @wtw - exactly - 

wtw said
........This is actually a major part of what I like about playing. It can get very relaxing, emptying your head, being here and now playing and listening to the music.

....The fun thing is I have a math/physics background too... but I'm totally the opposite in music. Can't get my brain to work efficiently at all, at least on a conscious level (so hoping it's not too lazy on a not-so-conscious level).  

Couldn't agree more !

Yes - this "auto-pilot mode" - I experience that on guitar as well - although over the last 4 years since I picked up violin - my poor guitars get very little attention !!!

A final tongue-in-cheek - and clearly false analogy to physics - a truly profound and exceptional performance is like the (impossible) breaking of the second law of thermodynamics - the reversal of entropy - we are making order out of chaos.....      - every scientist's dream....