In my experience, dumping syndrome is a catch-all for "we don't know what is going on but we are not surprised" side effects from the surgery, which in my case, included hypoglycemia years after the surgery. I have not been diagnosed with diabetes or pre-diabetes, which is, of course, the easy answer here.

I did recently (15 years after surgery) wear a CGM three times, for a couple of weeks each time, which was mildly informative -- it's important to be aware that no one really knows much about how to interpret CGM readings for people without diabetes, so we need to take them with a grain of salt. Especially and in particular, no one knows what glucose levels should be treated as abnormally low, or even how much volatility is normal. Also, over-the-counter CGMs are particularly unreliable for low glucose and more accurate for high glucose levels. (Which, when you think about it: fair. After all, high glucose is mostly what the technology was developed for.)

Also, in my case, the hypoglycemia was complicated by hypotension, which produces some similar symptoms and was fixed by eliminating statins from my polypharmacy. Fixing the hypotension really reduced the symptoms that had been attributed to the hypoglycemia.

Basically, if it's dumping syndrome, then the solution seems to be behavioral, which is to say, diet and exercise. I've added a LOT more fiber into my diet, which is a bit tricky when you aren't eating all that much in the first place. Also, since the problem seemed to be linked to morning migraines and overnight glucose lows, I started eating something with protein and fats (no carbs) immediately before bed (eg, hard boiled egg). If I were a better person, I would be exercising more regularly as well. In general, prioritizing protein and fats helps both the lows and the volatility, but I'm sure you are already doing that.

Sounds like they are trying to rule out the possibility that it's not dumping syndrome, though. If you haven't read this, you might want to: https://www.ncbi.nlm.nih.gov/books/NBK573079/.

I've recently been through a hunt for the basis of new peripheral neuropathy, and I have to say that the key thing I did was not to settle for "idiopathic". I was really stubborn, which finally led to a zebra diagnosis -- that is, something they swore to me in the beginning would not be the problem.

Ask them what they think the most likely causes are based on your symptoms/history/drugs/OTC supplements, how they expect to rule each cause in or out, how long it typically takes to diagnose them, and what you should be doing in the meantime to manage the symptoms. You should also ask whether there are any causes, regardless of likelihood, that should be ruled in or out as quickly as possible because delay could make treatment more difficult. (Beyond that, any discussion of low-likelihood possibilities can probably wait.)

You might also ask if there are mimics that could be causing your symptoms other than hypoglycemia, and that you should be exploring with some other specialist at the same time you are digging into the glucose issue. I can attest that this is possible.