I have POTS and most likely hypovolemia as well because salt water helps my symptoms a bit, but my blood glucose is in normal range. A friend gave me her old blood glucose meter a couple months ago and I've been measuring it before and after eating, because I noticed earlier this year I get weird reactions from carbs and started keto diet. Yesterday I wanted to see what happens if I drink sports drink with glucose in it, but it only raised my blood sugar to 7.4 mmol/l an hour after drinking it and in another hour the reading was back to my normal 5.4 (it's usually 5.1-5.4). So I'd say your problems stem from the diabetes and not from POTS. AFAIK keto sometimes helps with type 2 diabetes but I'd still recommend talking to your doctor about it.
I am eating Keto style meals now and am watching my glucose positively effected.
My doc put me on Keto 4 yrs ago (for other reasons), and I was on it for a year, and I noticed that my blood glucose was constantly good.
However, after a year on Keto, I sensed that it wasn't good for me overall. I am convinced that it developed insomnia issues for me from which I am still suffering. I'm doing Keto meals now just to get my bg under control, then I'm seeing my dr.
One thing I have done is cut out eating snacks between meals - I actually was eating good snacks like nuts, but I think this was stimulating my insulin. Plus I think I am releasing too much cortisol because I have problems getting into parasympathetic state.