As you get used to controlling your glycemia, your body starts to get used to living with its new levels of blood sugar and you get more attuned to the signs of an abnormal variation.
In my case, when my blood sugar goes above 130mg/dl, I get a dull headache. It’s not painful like a migraine, it’s a headache at the limit of perception. I know its there, but it doesn’t get in the way of day to day living. It’s hard to see how I could live before at 250mg/dl+ without noticing.
When my blood sugar drops below 80mg/dl, which has only happened a few times in the last few months, I feel light headed. I know my body is lacking glucose and I need to eat something.
Your signs might be different, but no doubt you’ll be able to feel when things aren’t right.