Did you miss the first posts in this series? Catch up before reading on!
For me, the single factor that leads to most of my unexpected low blood sugars and those occasional high numbers is forgetting to account for my activity level. Insulin works so much more efficiently in an active body than when we're sedentary. In order to bolus accurately, you have to consider how active you'll be while that insulin is working.
Nearly every weekend our family takes one or two long walks around our neighborhood or Balboa Park. When I carefully plan my insulin bolus and food intake with a walk in mind, I can usually manage my blood sugar quite well. I'll usually plan to give myself less insulin for my breakfast, lunch, or snack (whichever occurs before our walk), and drop my basal rate for an hour prior to leaving. This allows the walking to lower my blood sugar gradually since I won't have too much insulin-on-board.
However, if I don't plan, I end up low after 30 minutes of walking and have to snack frequently to keep my blood sugar stable. The worst is when I test just as we're heading out the door and discover that I'm in a low range. I gobble down a granola bar or a handful of dried apricots as we leave, but inevitably end up low after a mile or so. Because I didn't plan, the walking helped lower my blood sugar faster than the food could raise it.
Besides exercise, I'm noticed that cleaning lowers my blood sugar incredibly fast! We tend to do our chores around the house on weekend mornings. Even after a big breakfast, if I don't plan for it, I will end up with low blood sugar within an hour of starting to clean our place. It's something about the constant activity that just plummets my blood sugar! Again, planning ahead and bolusing less for the meal prior to this activity makes a huge difference.
Another activity that is almost guaranteed to drop my blood sugar is shopping. I test my blood regularly in the grocery store! Again, I think it's the constant activity of walking around a store or running several errands back to back, that work to gradually lower my blood sugar. An afternoon of shopping and errands demands a little more attention to how much insulin I'm bolusing that day.
Sometimes the issue isn't an increase in physical activity, but a period of extended inactivity that leads to unexpected blood sugars. At work, my days can be very physically active, where I'm away from my desk assembling tax returns or financial statements for long periods of time on my feet. Other days I'm sitting at my desk for hours on end. Some days are a mixture of activity and periods of sedentary tasks. When I bolus for my morning snack, lunch, or afternoon snack, it's really helpful if I know what the rest of my day holds. If I know I'll be rushing around and on my feet, I can bolus a bit less for my morning banana. What happens more often is that I'll have a higher than expected blood sugar after sitting for several hours. I suppose my default assumption is for a certain level of physical activity, thus those sedentary days really cause my blood sugar to rise.