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I know exactly what you mean. I have not hit that point on the violin yet, but I have experienced that several times over the years on guitar and some other instruments.
This is just my take and thoughts as to what happens: We spend a lot of time learning different techniques. After a certain point, we have them ingrained enough in our brain and muscle memory. At that point, a shift starts happening and we focus less on the actual mechanics of playing. That's when we start feeling the music and it starts coming out and on the next level.
And sometimes it slides back a little, but once it's there, it's not gone and just becomes more regular and consistent with continued practice.
For myself, I have learned not to over analyze it too much and just enjoy my progress at the new plateau. If I do, it just gets in the way of playing again.
Those are just my thoughts on the process. Congratulations again, and enjoy it.
I know how that feels @Mouse … enjoy ! Whether or not it goes back to what it was before (these instruments are fickle little things after all ), your brain and body will know what it's supposed to sound like and what being relaxed feels like. I think you'll be able to catch that state more and more often.