Dear mikes101,
Your "random thoughts" are indeed the result of stress release. They show how effectively NSR is lowering your metabolism so your nervous system can finally get the deep rest it needs to dissolve stress (see
http://www.nsrusa.org/about-stress.php).
"...sometimes with a bit of a jolt"
We don't realize how slowed-down our mind and body are until we see the contrast with the surface (concrete) level of thinking. At the end of your daydreaming, the jolt was the contrast with the more energetic level known as wakefulness. This is one way we know from our experience that transcendental consciousness is a unique state of the physiology (another way is from the accumulated research on Transcendental Meditation that shows this effect of transcending through actual laboratory measurement; see
http://tm.org).
"The syllable is usually more obvious at the start of the meditation..."
Naturally, since we are starting it from the waking state of consciousness. We can experience it more clearly, like "problem-solving" thoughts. But right away it refines, becomes more abstract, or even disappears. This is its nature as a vehicle for deep meditation.
"...most of the time goes along with my heart beat (sometimes with the breath). Often I feel the heart beat in my head along with the syllable."
These are normal experiences in the early days of practicing NSR. We're not in any kind of trance; we're aware of activities around us and in our own body. However, as time goes by and some of our stresses are eliminated, we find these activities less interesting. They capture our attention less. When we start experiencing unbounded inner bliss, the outside world simply can't compete anymore. We then appreciate our true nature as powerful, compassionate beings.
But, don't forget, this wonderful and transformative experience can only happen when the stresses are really gone. So always be satisfied to have various side effects of stress release. They indicate that something very good is happening.
David Spector
NSR Meditation/USA