Serratus anterior, huh ?
This again a new thing.
If I stick to this forum long enough, all your base will belong to us, InnerAthlete.
To not be totally off topic: migrenes also can be the effect of toxic byproducts of digestion, exposure to bright light (screens of al kinds). Sometimes the ill effects lurk beneath the surface of perceptible, and become apparent when awarness increases, or by slightly increasaed physical activity. In this case I recommend doing nothing:
I sometimes just lie down on my back, and I am not doing anything. Not even relaxing, or savasana, or breathing, but this is also not consciuous. And in this situation, I just do some movements, and I am just letting the body rearranging itself. Sometimees I feel like I am doing setu bandhasana, sometimes I do reclined bound angle. Sometimes I do modyfied poses I never heard of, and later I see them on some yoga site. No mental focus, nothing forced, the mind let to follow it's course. It is not important. It is important to develop a certain awarness, what is not the mundane clear focus, but a ceirtan detachment, even from asana practice, physical exercise, breathing, anything. It is hard to describe it, but it is very refreshing. I am calling it doing nothing, but it is not on purpose, if you know what I mean, because in fact I do things, but not with premeditation or aim in them. It is not yoga in the sense that is no aim in it, or any rule, or succestion. I am not doing to do this as yoga, I am doing it after I did my set, and before the final savasana.