Hello Anthem:
If automatic yoga (movements) become a distraction to the practice we are doing, or a physical hazard (in rare cases), we should temper them accordingly. We always have the option to choose what is in the best interest of our practice. While automatic yogas are generally a good sign of the interconnectedness of yoga within us, in the end it is our structured practice that will bring us home.
Of course, those who subscribe to the "no path" approach will not agree. Nevertheless, it is structured practice that fosters automatic yogas, not the other way around. The same goes for all experiences that arise when doing effective yoga practices. The experience is not what will transform us -- the practice is. The same goes for automatic yoga, though the line may be a bit blurred in that case. Still, experiences and automatic yogas are both effects of practice, not causes. It is good to keep that in mind, lest we put the cart in front of the horse.
The best approach to automatic yoga is to utilize it during corresponding structured practices we are doing. For example, if we are experiencing a tendency for head movements, we should not favor this excessively during our meditation -- best to favor the mantra. Better to favor the movements during chin pump practice (if we have added it to our routine), which is a good time for utilizing automatic head movements. As always, we should also apply self-pacing as necessary to regulate the build-up of our practices and correct any excesses. In these ways we can use automatic yoga while keeping structured practices in place.
In the case of siddhasana, we may be squirming around a lot during the formative stages of it, with all sorts of movements. These are normal and may represent identifiable automatic yogas or not. As siddhasana settles in, the movements will subside, transforming to an experience of much more refined internal ecstatic currents -- an inner fountain of ecstasy. This is another aspect of automatic yogas -- they settle down once the inner pathways involved have been opened somewhat. In this settling down, the immensity of joy residing deep within us will emerge.
Whenever we are dealing with automatic yogas or other manifestations of purification in the nervous system, it is a fine balance to allow the expression of our awakening inner energies, and at the same time maintain good forward progress through structured practices. It is like driving a fast car. We'd like to go as fast as possible, while operating within our present abilities so we can stay on the road and reach our destination. Varooom!
The guru is in you.