OK, so about the fitness stuff, I am very built, in very good shape. I have a mountain race coming up next month, and have been climbing from sealevel to 3000 or 4000 feet a couple times a week.
I did notice something last week though. I work at the Alaska Sealife Center, and was bent down looking into a microscope, I noticed that in this position I had the same uneasyness with my body. A seemed wavering, which brings me to wonder about anything I may be able to do to bring my concentration more together and not just to what I'm looking at but also to my body. My arms when shooting stay fairly stable, it's an overall imbalance. I do a lot of hiking across extremely rocky terrain, and have good balance, but only in this up close situation do I have the swaying.
Wasn't saying you are out of shape, not at all. What I have found out the hard way though, is that you can be aerobically in shape (I like to swim everyday; I'm up to 550 meters this summer with more to go), but have a very weak "core" of abs, gluts, and back muscles which will impact your balance. Ever worked with a therapy ball, or done a quantity of leg lifts and butt burners? You would be surprised how far you need to go with these, as compared to how far you are (literally) going when you run.
I'm a grad student, doing a nutritional and metabolic study of mule deer via plant cell identification in feces. Also, blood and liver tissue analysis of the same deer for my doctorate. My point is that I use a microscope and other lab equipment also, and probably assuming the same postures as you when working as well as when shooting. I noticed the wobble too, especially after back surgery.
The core strengthening that I've had to do as a result of back surgery has helped with my balance, stamina and as a "fringe benefit", my group sizes have shrunk. I'm not talking about getting a "six pack" either. What I'm talking about is strengthening the muscular "girdle" that helps to keep us erect. It works because I can keep my torso more stable without an external support. That is what you are looking for, especially when you are croutched over a microscope.
Even though you it sounds like you are in great shape, you would be surprised how weak these muscles can be - I have seen runners crippled up because they bent over to pick up a gum wrapper and their back went out because the muscles are weaker than they should be. Something else to consider- the biggest muscle in the body, and most under-utilized but most important for posture, support and stamina are the gluteal muscles that we sit on. :-)