Hi, anything below 4.0 is technically a hypo when you do not have a fully functioning pancreas, as the body's mechanisms cannot necessarily prevent it falling lower whereas a healthy pancreas would. We have a few members who have had some or all of their pancreas removed so they should be able to provide you more specific information there. Try not to worry too much about falling to levels in the upper 3s, just make sure you have a small amount of fast acting sugar if it happens like a couple of jelly babies, glucose tablets or some full sugar coke/lucozade to bring your levels up again. Might be worth having a biscuit or small snack before leaving work, and if you drive home you should certainly test and make sure you are above 5 before doing so. What remains of your pancreas may have started producing more insulin, or perhaps the metformin along with any adjustments you have made to your diet or lifestyle may mean you have become more sensitive to the insulin being produced.
LADA, or Type 1.5 is Late onset Autoimmune Diabetes in Adults, and is like a slowly developing Type 1 where insulin production gradually declines and leaves the person needing to inject insulin. It's probably what I was, although I didn't get diagnosed until I had already reached the 'needing to inject' stage (hadn't recognised the symptoms developing over the previous two years).