hi
whats dangerous with circulation?
i think zazen also opens the microcosmic orbit by concentrating at the dantien only.
so i see there is no danger, if you concentrate on your dantien and breath naturally.
also you can count your breath.
look here:
http://www.boudicca.de/qigong-e.htm
earthing is also a good start to nei kung.
let the chi flow through your hole body from the top of the head down to the feet and out of the feet. visualize roots coming out of your feet down in the earth.
but i see there also no danger with microcosmic orbit meditation.
regards
laotse