What you described is very familiar to me as well. It can last long after the other anxiety symptoms have gone away. For me I think it's due to tension in my jaw and neck (I clench my jaw when I'm anxious without realizing it, and I even do it at night). I think this puts pressure on my inner ear and causes the feeling of disequilibrium/imbalance. Also, anxiety can directly cause me to feel like my legs aren't steady, like they don't quite move on cue. It can do this with my hands as well. If I let it freak me out, it gets much worse very quickly. If I can take some breaths and relax, it helps (though the disequilibrium/imbalance can continue for days and sometimes even weeks or months). Like Kmj023, I think there may be a component of seasonal allergies contributing to it as well. It does affect me more when my sinuses are bad.