I guess it's human nature to have a drive to change your consciousness. After I experienced a consciousness shift without drugs, I wanted to be inside of this state all the time. As a teen, it was pretty quickly that I noticed the paradoxes involved in trying to get to any particular state of awareness.
What seems to jog a change in consciousness to happen for me is a sudden change in perception - the change can be very slight. I believe that this is why AT jogs me into this state so easily, but not every time or in every instance. It's just that I suddenly notice I am there again, always new, but strangely familiar - as in an absence of habit, like AT can sometimes reveal and make unfamiliarity stick for a longer and longer moments. If I would go do something with my habits, the state of grace would go away.
For me, it's as if the state itself is always waiting for me to notice it, and I am merely too distracted for it to come to me, like it's a lover who has always loved me and I've forgotten he's there because the love is as natural as breathing.
Something about rain or the sound of water still makes me susceptible to my awareness suddenly opening up to perceive what has always been there. A refrigerator suddenly stopping its motor can do it. Suddenly noticing the steam curling up from a cup of tea. Last night at midnight I was socializing with friends by a fire, and my consciousness shifted once more - my ear suddenly opened up! I did not even notice that my hearing had been closed down. It was the same thing that happens when your ears pop from a change in altitude. But it was so much more than that. Becoming so aware suddenly after my ears popped put almost an auditory shine on each sound.
One time I had my eyes dilated, and what happened for me afterward was absolutely psychedelic for quite some time! It's sometimes quite laughingly funny and also weirdly funny how and when these little times occur. To sustain them it takes being able to completely suspend for longer and longer times. To just be happy to think less; tie the thought to the act it is for and leave the rest alone quite purposefully.
I imagine that is how zazen works, to quiet your thinking, direct your thoughts to pause for moments and then stop for a longer moments. I think that making music also has this effect, as it seemed to happen for me as I began to internalize rhythm; then I
began to internalize silence for longer and longer rhythm patterns. It seemed to me that rhythm patterns can have such a long repetition durations that nobody can hear them twice...
Other times a surprise can trigger this opening up - such as the surprise of beauty, gratitude, an exquisiteness of awe or discovery, or just plain old curiosity. Absorption is another quality that can help the state to happen. I've suddenly experienced epiphany while playing pool. I suddenly could not miss any shot I tried, because I had already seen where the balls would go as if I was some sort of fortune teller or master programmer of a billiard video game!
The important part is that I can only watch for this state of grace, and pay attention some more, and more, and not be upset that it hasn't come to me if it isn't happening. Because being upset hides it, being analytical hides it, most other states that I can be in, they all hide its quality too. It seems to be the absence of all qualities.
I've learned that sooner or later this state of grace will come to be again, like someone's name I've forgotten, a familiar smell triggering a charming memory, or a certain sense of deja vu.
I'm not sure why this is the way it is for me, but there you go.