The best understanding I ever read was from a paper back book when I was diagnosed with low blood sugar. It showed charts on how the blood sugar goes up and down over a 24 hour period. It is not just the sugar food but the amount of fat in the food that helps determine how high the blood count goes. With fat, as in peanut butter, the rise is slower and it takes longer to digest. Your sugar level was perhaps in the down level so it was probably going down despite the rice checks. I really don't know how the blood acts in the middle of the night, but I have had the same experience of eating in the night but I never check my blood so soon after eating. The 212 number could have been caused by the cortisone shot, depending on how long it stays in the blood. I haven't studied that.
Just know that the blood sugar is going up and down, rising two hours after eating, and then dropping, and then starting back up again but not as much on an empty stomach. I was told to eat something at bedtime, to get the metabolism working, but then after the food is digested, I can get hungry in the night.
You will need to read a textbook to get some understanding of the whole process, I believe. Your best help comes from a certified nutritionist. Even then, she handed me a book and I had to study on my own. I will try to find something because I am interested in the matter myself. I am trying to go more than twelve hours at night before eating breakfast. I would like to sleep like a log all night, but that isn't happening. I am working on it. Medicare paid for my expensive consultation with the nutritionist, by the way.