Eating Out And Night Walking Sugar Plummet

Visitors came from America during the week. There was a bit of a get together in Ballybunion. We ate in a place called Coast. I had an open tuna sandwich with toasted gluten free bread. There was no reaction, which was excellent. So I might eat there again if ever I need to eat out in Ballybunion in future.
A few days beforehand I went for a quick trip to the shop after supper. I was above 10 when I tested before supper so I took one extra unit of insulin on top of my usual supper dose. What I was looking for wasn't in the nearest shop so I went to where I knew I could get it. As I approached the second shop I could feel that I was low. This was probably less than an hour after my blood sugar read above 10 and after eating supper. I took a few glucose tablets before going in and tested myself outside the shop after I had bought what I needed and a snack to munch on. I was still 3.5 after the glucose tablets so I don't know how low I actually went when it felt like my legs were turning to jelly before taking them. If I hadn't gone out walking while it was dark I might have been above 6 when testing before Lantus three hours after supper. Whatever it is about walking in the dark, my blood sugar always seems to plummet. Hardly ever falls that fast during the day. I also only had one strip to test myself so I had to go by how my body felt for deciding when it was ok to walk home. I'll have to be cautious of going walking during the winter nights.