Los, there is only one real way to find out if you have low aldosterone. Do the flashlight test! It's in Wilson's book and on the Web. The tests basically tests your pupils levels and times of dilation and constriction.
CHECK IT: It seems sodium regulates the eye's sphincter muscles in the iris (iris is a little ring around the pupil that 'opens' and 'closes' the pupil). When low on sodium, muscles are too weak to properly constrict. With the pupil staying dilated, too much light hits the optic nerve, and voila-a migraine headache!