There is both natural asymmetry in the body and asymmetry born of the body’s compensation for your daily habits of movement and rest. For instance, most of the major pronouncements of the right side of my body are just the slightest bit lower than the left side, since birth. If I am working at a desk a lot, I tend to lean to the left which results in tension in my left neck and weakness in my right. If I don’t attend to it, I can sometimes get a spasm in my neck. I’ve also been in a few car accidents and so the spine in my neck area is slightly off. This is something that my body compensated for by creating extra tension in my neck and back, and the proper application of the RIGHT yoga practices really showed me how to strengthen the areas needed to bring my body back into a functional balance.
With the help of a proper teacher who can look very carefully at you, it is possible to determine whether they slight differences you notice are going are possibly going to cause you any problems, or whether they are simply just your natural state of being. Someone trained in observation could watch you get into these positions and stay in them, and better see your muscle tone and tension and where your strengths were. If you are in sirsanana and trying to look in a mirror, you really can never get a truly accurate assessment of what is out of alignment, primarily because your perspective is only from a viewpoint in which you should be focusing on your breath and looking at one spot to keep your balance, not having your eyes dart all around your body to measure it. Sirsanana is a hard posture by itself, and one could expect imbalances in the body to show up here that do not show up in other postures because the body is not accustomed to a reversal of gravity. Working with someone else to observe you would also give you insight into what imbalances exist in other, even simpler postures, that are indicators of weakness or compensation in the body. When I did my teacher training, we did our primary observations in postures such as tadasana, savasana, uttanasana, and just seated- while having people raise and lower their arms with the breath. These very simple postures made it possible to see an incredible amount of structural imbalances, and once these foundational inconsistencies were worked on, they were much more comfortable trying some of the more challenging asanas because their primary problems had been addressed. I suggest having a teacher with a good eye help you out with this. There are ways to help the body adapt more functionally to these asymmetries, but as I said above, only a good witness could tell you whether or not it is needed.
