Did my usual post-prandial test 2 hours after sitting down to a Southern Fried Chicken Salad (35g carb according to my carbs spreadsheet) and got 3.7, which I thought couldn't be right. Switched hands and did a second test, 3.8, so picked a third finger and got 4.0 - so I guess I really was that low.
Feel completely normal, though. Bizarre. The only time I've got remotely near that level in the past is after a post-meal walk.