I don't think you would even notice a slightly reduced FEV1, everyone loses a little pulmonary function as they age so you are probably fine but you can verify that with your upcoming appointment.

I noticed you had a thread about anxiety, that can really cause shortness of breath too. I was wondering how long you have been on Synthyroid and how long its has been since you had your thyroid levels checked? Mrs D probably knows a lot more about that than I do but I think having your thyroid level too high can cause anxiety, does your heart race? Or you might have something interacting with something else, I noticed Neurontin can rarely cause shortness of breath and anxiety too but I don't know if its common enough to consider.

Hope you figure it out.
judi