I've seen 2 specialist endocrinologists over the last 2 years and they both diagnosed me with idiopathic reactive hypoglycemia. After doing a lot of tests. The first endo tested for insulinoma but the second endo said the test should have been done under fasting conditions and the only way to really find out is a blood test when bgl is below 3.0. She has confirmed the RH diagnoses and suggested a fasting test for insulinoma. She said because I hypo quickly when fasting I don't need to go to hospital for 3 days but to do a fast at home and get someone to drive me to the pathology clinic when my bgl is lower than 3.0 to do the relevant tests. She gave me the forms I need to do that. She said it's to rule out insulinoma and she said it's so rare it's very unlikely to be that. She also said my condition is very unusual and would love to see a study done into RH and keto diet as it is obviously working so well in my case.
Regardless, I would still do it! I would ask your GP to help with the test, if there is no other way! Any tests like this, were the patient is likely to go hypo, should be supervised. A 72 hours fasting test is the final step in diagnosis, and I'm certain, that if you don't go hypo, like I did, then RH is diagnosed. If you do go hypo then further tests are required, to see if it's insulinoma or another pancreatic condition.
The reason behind RH, is that it is food related, and food will trigger the reaction. Not having food, should not cause a hypo. Unless it is another type of hypoglycaemia or has been said previously.
You could have something similar to RH with T2, when, you have diabetic numbers fasting and hba1c before the overshoot develops over time.
The treatment is the same, a ketogenic lifestyle and staying hypo free.
Insulinoma is rare but it shouldn't be ignored by your specialist.
Reactive Hypoglycaemia is also very rare, and yes, there is not enough research done, I myself was used as a guinea pig in having a lot of eOGTTs to help my specialist endocrinologist write a paper on how a drug can help with control. It didn't stop hypos and it wasn't a cure, but nevertheless, my specialist did help me understand the condition and how it works, and why!
Overall, idiopathic should not be used in diagnosis, because if they understood the way food caused the trigger and hypo, it is not unknown. The only reason it could be used is why we have a very weird and rare overshoot, because not many conditions have this, I have been called weird by doctors, especially those who don't understand it!
Keep safe.