Nadis are integral to the chakra/kundalini system. They are tubes of astral matter, through which a type of energy flows. There are believed to be about 72,000 nadis for each person. They exist within the astral body, vigyanamaya kosha, which is where the chakras reside within. Satyananda Yoga says that they are part of the pranic body, pranamaya kosha, & this may be correct, however they do have a different energy from the pranic body. The different kinds of prana within the body, even when awakened, have a different quality from the awakened nadis.
These nadis have energy streaming through them. Within the astral body, & also in the aura. In the aura, they can waft in the breeze, so to speak, like seaweed moving in the ocean with the movement of the currents. I do believe, from my own experiences, that the differing types of nadis, are in fact, currents. The more aimless we are, the less strong these nadis are, in the aura. And the more we learn to focus, the stronger the nadi energy, which will still not be properly awakened, the stronger this energy grows within us. When our awareness is all over the place.....our energy, in these nadis, it too is "all over the place".
We have many nadis. We have the meridian lines of acupuncture, nadis which are related to the chakras, nadis in the brain, nadis running alongside & intersecting the spine, &, most famously, the main nadi inside the physical spine. The nadis within the brain, like channels of the mind-space, purify, so that more prana, at first, can flow, unimpeded through these channels. This happened to me prior to the proper awakening of the pranic body, & was consistent with my swadhisthana (2nd chakra) period. Manipura chakra awakening quickly followed the awakening of the pranic body. (that same evening). However I taught a woman who had an evening when energy was simultaneously streaming up & down the 2 nadis alongside the spine & the spinal nadi for quite some time, a truly auspicious happening.
If we look at the nadis...they do have to "wake up". So, first of all, they do exist, they do have energy in them...but......another sort of energy must awaken within them. The nadis, except for sushumna, the main "spinal" nadi, are all electrical in nature. Prana is not electrical. The nadi electrical energy can shoot all through our astral body, when it awakens. This was a difficult period for me when it started to happen, I did not realise at the time what was actually going on. My whole body expanded, I felt like a sheath which was black inside with crackling electrical energy shooting through this space. It hurt. I was teaching a lot of spiritual yoga & when I was teaching I would overheat, I even got "burns" on my body, my digestion didn't work. I felt as though my body was failing me. I wondered if I had a disease. But it did all eventually calm down once this electrical energy had established itself, especially after a big awakening one night. The kundalini had been awakened for some years, the kundalini energy had travelled up to sahasrara during this electrical period. But the 2 secondary major nadis, the 2 intersecting the spine where the chakras reside...these 2 energies had not electrically awakened. One night, I was awoken by the loud sound of sizzling electrical currents. One was a red current, one was blue. As they sizzled, they quickly touched...the a massive explosion....& the electrical energy of these 2 currents was well & truly active. A stronger electrical energy than that of the other nadis.
Spiritual awakenings are not for the faint-heartened! The prana body awakening is a big experience, so are the nadis, the red & blue energies are even stronger, but the mighty kundalini is the strongest energy of all, it is a big happening & far exceeds nadi energy.