One of my favourate guitarists said "I think when we are playing music we try to become the music. One should begin a piece of music and wake up at the end having become that music... becoming one to flow with it. This takes a deep understanding of the music".
It was very hard for me to explain the feelings of playing music but this is probably the best explanation. You play music and become it flowing through the notes. You wake up at the end feeling like you have been on a great journey. The most relaxed I have ever been was after playing a Barrios piece on guitar. I still remember it.
Anyways... when I saw this video it reminded me of that feeling. The whole piece is nice of course. If you are unfamiliar with this piece of music I highly suggest watching the whole thing... it may change your life. When you listen to it, concentrate on listening. If you really want to get the full appreciation devote 100% of your attention to it. But if you just want to get my point watch from 6:30 to the end. You can really feel the anger and struggle in the music. I can hear the composer going crazy and trying to figure out an answer to his problem.
Right at 7:30 when she finishes the piece, look at her. She is literally waking up from a self induced trance. I cannot explain such a feeling... it is something you have to experience for yourself. Enjoy!