I think it is important to remember that everyone's physiology is a bit different, both from the point of view of how your body is put together and deeper more mysterious processes ("karma" , level of soul advancement, degree of ponerization, and so on). And, no single physiological experience I think is a clue to one's inner level of awareness.
Any technique should be understood as merely a techniquer (albeit perhaps extremely important in our training) and not something that needs be masteed with our subjective understanding of perfection.
In my opinion, a technique must become a living gesture of our being rather than followed with mechanical precision---EXCEPT that deviations from the mechanical prescription should, in this case, be cleared through the process of networking.
So, people have mentioned having a speeded up heart rate, pain in the abdomen, blurry vision and others. I suggest that any of these signals are signs that you should stop, give it a rest, and do it again a day or two later. So far, people have mentioned the mere physiological but soon there will be emotional and mood experiences. In all such cases, we need to be really kind to ourselves and not push. Just relax in the joy of discovering a new layer of intelligence and responsiveness. Back off the practice, if need be and just go with the prayer, for example.
Speaking for myself, I too experienced a quickened heart and, not a pain in the abodomen, but a kinda of pleasant bloatedness. I am rather near sighted and when I do the practice, my vision clears and becomes much sharper.
In another context, i underwent training at a week long retreat about a year and half ago that used very similar techniques and midway, huge emotional issues erupted. When that happens to you (and it will), just stay with the experience and feel its rawness without trying to justtify or rationalize it. You may even experience extreme doubt about what the hell you are doing--that too is part of being clear and honest with oneself in the midst of almost, through this kind of practice, creating a self-mirror.
OSIT---Frank J.