I had an under 60 result once. I didn't even know about it until years later when I had changed doctors and he gave me access to all my previous results. It was never retested or followed up on in any way. It has returned to normal now.
One doctor did explain to me that the rate of change can be more important than the actual level itself. My GFR fell 11 points in 3 months and you can bet I was messaging both my primary care doc and the endo asking for follow-up. I don't know what part medications or inactivity can play. A GFR of 57 is far, far away from needing dialysis though.
I don't have any of the lightheadedness associated with POTS - that seems to be a significant symptom in those who have it.