Over the last two weeks I've started to develop rapid onset hypoglycaemic episodes.

These are very different from dumping and seem to happen about 20minutes into a meal and I become drowsy and confused. Fortunately the situation resolves with a piece of chocolate or glucose tablet but means I'm having to eat more chocolate than I'd like and that's screwing up my weight loss which had finally got back on track.

I've read up on it and it's a rare complication - http://www.healio.com/endocrinology/diabetes/news/print/endocrine-today/%7B1dc23215-49dc-4ad7-90da-346ba16663d6%7D/post-gastric-bypass-hypoglycemia-a-serious-complication-of-bariatric-surgery

It seems it's a known late complication of RNY and I'm getting it investigated to rule out insulinoma but wondered if anyone else had experience of it and had any tips on managing it?

Several individual on this site have reported the condition. It is officially called "reactive hypoglycemia". Here is a link to the condition and the recommended approaches to deal with it. http://www.mayoclinic.org/diseases-conditions/diabetes/expert-answers/reactive-hypoglycemia/faq-20057778

For the majority of people, reactive hypoglycemia usually doesn't require medical treatment. It may help to pay attention to the timing and composition of your meals:

* Eat several small meals and Snacks throughout the day, no more than three hours apart during the waking hours.

* Eat a well-balanced diet, including lean and nonmeat sources of Protein, and high-Fiber foods, including whole grains, fruit and vegetables.

* Avoid or limit sugary foods, especially on an empty stomach.

* Be sure to eat food if you're consuming alcohol and avoid using sugary soft drinks as mixers.

It happens when I forget to eat

As a former diabetic, I would caution you against using chocolate to resolve it. We were told in diabetes education not to use chocolate as it takes too long to process and has too much other stuff. So, a glucose tablet is good or a peppermint candy or a very very small amount of juice, etc. Now I don't know if reactive hypoglycemia has different needs than hypoglycemia caused by diabetes but it seems to me that the same rules for increasing your sugar may apply though likely in smaller amounts so as not to lead to dumping.